Detect security plugin presence and improve WLM rule error message

[dzane17]

Description

Saving a WLM rule with a username or role on a cluster without the Security plugin currently fails with this cryptic error:

Failed to save changes: [x_content_parse_exception] principal is not a valid attribute within the workload_group feature.

This PR detects whether the OpenSearch Security plugin is installed and active. If it isn't, the Username and Role inputs are disabled with helper text "Requires the OpenSearch Security plugin to be installed and enabled on this cluster." If a save still surfaces the cryptic backend error (e.g. on a slow probe or stale state), it's rewritten to that same actionable wording.

All inactive states are covered: not installed, installed-but-disabled, plugin reachable but degraded, and probe failure (in which case the UI does not over-block).

Screenshot

Issues Resolved

Closes #530

Testing

• New WLMDetails.security.test.tsx covering each plugin state and the rewritten save error.
• Extended datasource-utils.test.ts and WLMCreate.test.tsx with the same coverage on the create path.
• All 470 unit tests pass; lint and typecheck clean.
• Manually verified on a local cluster with only the workload-management plugin installed.