[ftr] read username from config (#169755)

## Summary

Similar to #169639

The tests fail on MKI because username is hardcoded to
`elastic_serverless`. Reading value from FTR config should fix it.

x-pack/test_serverless/functional/test_suites/common/reporting/management.ts

@@ -17,6 +17,7 @@ export default ({ getPageObjects, getService }: FtrProviderContext) => {
   const retry = getService('retry');
   const PageObjects = getPageObjects(['common', 'svlCommonPage', 'header']);
   const reportingAPI = getService('svlReportingApi');
+  const config = getService('config');
 
   const navigateToReportingManagement = async () => {
     log.debug(`navigating to reporting management app`);
@@ -47,8 +48,9 @@ export default ({ getPageObjects, getService }: FtrProviderContext) => {
       ],
     };
 
-    const TEST_USERNAME = 'elastic_serverless';
-    const TEST_PASSWORD = 'changeme';
+    // Kibana CI and MKI use different users
+    const TEST_USERNAME = config.get('servers.kibana.username');
+    const TEST_PASSWORD = config.get('servers.kibana.password');
 
     before('initialize saved object archive', async () => {
       // add test saved search object

x-pack/test_serverless/functional/test_suites/observability/cases/view_case.ts

@@ -28,7 +28,7 @@ export default ({ getPageObject, getService }: FtrProviderContext) => {
   const cases = getService('cases');
   const svlCases = getService('svlCases');
   const find = getService('find');
-
+  const config = getService('config');
   const retry = getService('retry');
   const comboBox = getService('comboBox');
   const svlCommonNavigation = getPageObject('svlCommonNavigation');
@@ -453,7 +453,7 @@ export default ({ getPageObject, getService }: FtrProviderContext) => {
 
         const reporterText = await reporter.getVisibleText();
 
-        expect(reporterText).to.be('elastic_serverless');
+        expect(reporterText).to.be(config.get('servers.kibana.username'));
       });
     });
 

x-pack/test_serverless/functional/test_suites/security/ftr/cases/view_case.ts

@@ -28,7 +28,7 @@ export default ({ getPageObject, getService }: FtrProviderContext) => {
   const cases = getService('cases');
   const svlCases = getService('svlCases');
   const find = getService('find');
-
+  const config = getService('config');
   const retry = getService('retry');
   const comboBox = getService('comboBox');
   const svlCommonNavigation = getPageObject('svlCommonNavigation');
@@ -452,7 +452,7 @@ export default ({ getPageObject, getService }: FtrProviderContext) => {
 
         const reporterText = await reporter.getVisibleText();
 
-        expect(reporterText).to.be('elastic_serverless');
+        expect(reporterText).to.be(config.get('servers.kibana.username'));
       });
     });