[Security Solution] Readme files update (elastic#187596)

## Summary

We have been asked to stop using the `second quality gate` terminology
in favor of `kibana QA quality gate`. This PR updates the readmes to
reflect the new changes.

(cherry picked from commit 3065d56)

x-pack/plugins/security_solution/public/management/cypress/README.md

@@ -34,7 +34,7 @@ for more information.
 Similarly to Security Solution cypress tests, we use tags in order to select which tests we want to execute on which environment:
 
 - `@serverless` includes a test in the Serverless test suite. You need to explicitly add this tag to any test you want to run against a Serverless environment.
-- `@serverlessQA` includes a test in the Serverless test suite for the Kibana release process of serverless. You need to explicitly add this tag to any test you want you run in CI for the second quality gate. These tests should be stable, otherwise they will be blocking the release pipeline. They should be also critical enough, so that when they fail, there's a high chance of an SDH or blocker issue to be reported.
+- `@serverlessQA` includes a test in the Serverless test suite for the Kibana release process of serverless. You need to explicitly add this tag to any test you want you run in CI for the Kibana QA quality gate. These tests should be stable, otherwise they will be blocking the release pipeline. They should be also critical enough, so that when they fail, there's a high chance of an SDH or blocker issue to be reported.
 - `@ess` includes a test in the normal, non-Serverless test suite. You need to explicitly add this tag to any test you want to run against a non-Serverless environment.
 - `@brokenInServerless` excludes a test from the Serverless test suite (even if it's tagged as `@serverless`). Indicates that a test should run in Serverless, but currently is broken.
 - `@skipInServerless` excludes a test from the Serverless test suite (even if it's tagged as `@serverless`). Indicates that we don't want to run the given test in Serverless.

x-pack/test/security_solution_api_integration/README.md

@@ -22,7 +22,7 @@ we have introduced the `detection_response` directory to consolidate all the int
 
    * `@serverless`: Runs in the first quality gate and in the periodic pipeline.
 
-   * `@serverlessQA`: Runs in the second quality gate.
+   * `@serverlessQA`: Runs in the Kibana QA quality gate.
 
    * `@skipInEss`: Skipped for ESS environment.
 

x-pack/test/security_solution_cypress/cypress/README.md

@@ -45,11 +45,11 @@ Please, before opening a PR with the new test, please make sure that the test fa
 Note that we use tags in order to select which tests we want to execute:
 
 - `@serverless` includes a test in the Serverless test suite for PRs (the so-called first quality gate) and QA environment for the periodic pipeline. You need to explicitly add this tag to any test you want to run in CI for serverless. 
-- `@serverlessQA` includes a test in the Serverless test suite for the Kibana release process of serverless. You need to explicitly add this tag to any test you want you run in CI for the second quality gate. These tests should be stable, otherwise they will be blocking the release pipeline. They should be also critical enough, so that when they fail, there's a high chance of an SDH or blocker issue to be reported.
+- `@serverlessQA` includes a test in the Serverless test suite for the Kibana release process of serverless. You need to explicitly add this tag to any test you want you run in CI for the Kibana QA quality gate. These tests should be stable, otherwise they will be blocking the release pipeline. They should be also critical enough, so that when they fail, there's a high chance of an SDH or blocker issue to be reported.
 - `@ess` includes a test in the normal, non-Serverless test suite. You need to explicitly add this tag to any test you want to run against a non-Serverless environment.
 - `@skipInEss` excludes a test from the non-Serverless test suite. The test will not be executed as part for the PR process. All the skipped tests should have a link to a ticket describing the reason why the test got skipped.
 - `@skipInServerlessMKI` excludes a test from the execution on any MKI environment (even if it's tagged as `@serverless` or `@serverlessQA`). Could indicate many things, e.g. "the test is flaky in Serverless MKI", "the test has been temporarily excluded, see the comment above why". All the skipped tests should have a link to a ticket describing the reason why the test got skipped.
-- `@skipInServerless` excludes a test from the Serverless test suite and Serverless QA environment for both, periodic pipeline and second quality gate (even if it's tagged as `@serverless`). Could indicate many things, e.g. "the test is flaky in Serverless", "the test is Flaky in any type of environment", "the test has been temporarily excluded, see the comment above why". All the skipped tests should have a link to a ticket describing the reason why the test got skipped.
+- `@skipInServerless` excludes a test from the Serverless test suite and Serverless QA environment for both, periodic pipeline and Kibana QA quality gate (even if it's tagged as `@serverless`). Could indicate many things, e.g. "the test is flaky in Serverless", "the test is Flaky in any type of environment", "the test has been temporarily excluded, see the comment above why". All the skipped tests should have a link to a ticket describing the reason why the test got skipped.
 
 Please, before opening a PR with a new test, make sure that the test fails. If you never see your test fail you don’t know if your test is actually testing the right thing, or testing anything at all.
 
@@ -304,7 +304,7 @@ Per the way we set the environment during the execution process on CI, the above
 For test developing or test debugging purposes, you need to modify the configuration but without committing and pushing the changes in `x-pack/test/security_solution_cypress/serverless_config.ts`.
 
 
-### Running serverless tests locally pointing to a MKI project created in QA environment (Second Quality Gate)
+### Running serverless tests locally pointing to a MKI project created in QA environment (Kibana QA quality gate)
 
 Note that when using any of the below scripts, the tests are going to be executed through an MKI project with the version that is currently available in QA. If you need to use
 a specific commit (i.e. debugging a failing tests on the periodic pipeline), check the section: `Running serverless tests locally pointing to a MKI project created in QA environment with an overridden image`.