Enhance access query logic to handle user ID and name conditions (ela…

…stic#202833)

[Obs AI Assistant] Fetch user instructions and conversation using user
id instead of user name -
elastic#192701

To avoid potential collisions when fetching data, we should query for
the user id instead of the user name when getting instructions or
conversations.

**If user.id is provided:**
  - Matches documents with user.id equal to the provided value.
  - Falls back to user.name when user.id does not exist in the document.
 
**If user.id is not provided:**
  - Matches only documents with user.name.

## Summary

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gif.


### Checklist

Check the PR satisfies following conditions. 

Reviewers should verify this PR satisfies this list as well.

- [ ] Any text added follows [EUI's writing
guidelines](https://elastic.github.io/eui/#/guidelines/writing), uses
sentence case text and includes [i18n
support](https://github.com/elastic/kibana/blob/main/packages/kbn-i18n/README.md)
- [ ]
[Documentation](https://www.elastic.co/guide/en/kibana/master/development-documentation.html)
was added for features that require explanation or tutorials
- [ ] [Unit or functional
tests](https://www.elastic.co/guide/en/kibana/master/development-tests.html)
were updated or added to match the most common scenarios
- [ ] If a plugin configuration key changed, check if it needs to be
allowlisted in the cloud and added to the [docker
list](https://github.com/elastic/kibana/blob/main/src/dev/build/tasks/os_packages/docker_generator/resources/base/bin/kibana-docker)
- [ ] This was checked for breaking HTTP API changes, and any breaking
changes have been approved by the breaking-change committee. The
`release_note:breaking` label should be applied in these situations.
- [ ] [Flaky Test
Runner](https://ci-stats.kibana.dev/trigger_flaky_test_runner/1) was
used on any tests changed
- [ ] The PR description includes the appropriate Release Notes section,
and the correct `release_note:*` label is applied per the
[guidelines](https://www.elastic.co/guide/en/kibana/master/contributing.html#kibana-release-notes-process)

x-pack/plugins/observability_solution/observability_ai_assistant/server/service/util/get_access_query.ts

@@ -17,12 +17,7 @@ export function getAccessQuery({
         filter: [
           {
             bool: {
-              should: [
-                { term: { public: true } },
-                ...(user
-                  ? [{ term: user.id ? { 'user.id': user.id } : { 'user.name': user.name } }]
-                  : []),
-              ],
+              should: [{ term: { public: true } }, ...getUserAccessFilters(user)],
               minimum_should_match: 1,
             },
           },
@@ -51,3 +46,23 @@ export function getAccessQuery({
     },
   ];
 }
+
+function getUserAccessFilters(user?: { name: string; id?: string }) {
+  if (!user) {
+    return [];
+  }
+
+  if (user.id) {
+    return [
+      { term: { 'user.id': user.id } },
+      {
+        bool: {
+          must_not: { exists: { field: 'user.id' } },
+          must: { term: { 'user.name': user.name } },
+        },
+      },
+    ];
+  }
+
+  return [{ term: { 'user.name': user.name } }];
+}