[Obs AI Assistant] Fetch user instructions using id instead of username for knowledge base instructions

[neptunian]

Given we already store the profile_uid as the user id, to avoid potential collisions when fetching data, we should query for the user id instead of the user name when getting instructions. Currently we get the current user in the request and query with internalUser searching by the username.

Some background from kibana security:
When usernames are created in Elasticsearch's native realm, usernames are unique. The issue is that these are unique only within this native realm. If on-prem or ESS is configured with multiple realms (e.g., native + SAML/AD/OIDC/LDAP, like in ESS where we have Elastic Cloud via SAML + native users who can log in via Kibana's native login form), then we can potentially have users with the same username living in different security realms. Generally, we recommend using the profile ID, which is globally unique across all security realms (it has certain limitations that you should be aware of though: #175431 (comment)

[arturoliduena]

@neptunian, If this issue relates to the code:

kibana/x-pack/plugins/observability_solution/observability_ai_assistant/server/service/knowledge_base_service/index.ts

Lines 361 to 364 in 3d3b32f

	getUserInstructions = async (
	namespace: string,
	user?: { name: string }
	): Promise<Array<Instruction & { public?: boolean }>> => {

could you clarify if the changes are needed in here:

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

Lines 7 to 25 in 4a16e91

	export function getAccessQuery({
	user,
	namespace,
	}: {
	user?: { name: string; id?: string };
	namespace?: string;
	}) {
	return [
	{
	bool: {
	filter: [
	{
	bool: {
	should: [
	{ term: { public: true } },
	...(user ? [{ term: { 'user.name': user.name } }] : []),
	],
	minimum_should_match: 1,
	},

Also, could you provide guidance on testing the solution? Any specific test cases or setup recommendations would be very helpful.

[neptunian]

Note: Check why the id is optional to make sure it exists. Id is provided by security as optional. Why?