Improve OpenSearchOps MCP endpoints for cluster debugging (new routes + better route descriptions)

[simcariou]

Summary

OpenSearchOps currently covers basic OpenSearch diagnostics, but it is missing several read-only endpoints that are important for advanced cluster debugging (tasks, recovery, node info, thread pools, cluster settings/state/stats).

Since these routes are exposed via MCP, the OpenAPI route descriptions should also be improved so agents can better understand:

• when to use each endpoint
• differences between similar endpoints (e.g. pending_tasks vs tasks)
• which endpoints may return large payloads

Requested Changes

1) Add new read-only endpoints

Add the following routes to OpenSearchOps:

• GET /os/cluster/settings
• GET /os/cluster/state
• GET /os/cluster/stats
• GET /os/nodes/info
• GET /os/nodes/hot_threads
• GET /os/tasks
• GET /os/tasks/{task_id}
• GET /os/cat/nodes
• GET /os/cat/allocation
• GET /os/cat/thread_pool
• GET /os/recovery
• GET /os/index/{index}/recovery

2) Improve MCP/OpenAPI route descriptions

Add detailed description= metadata to OpenSearchOps routes, with:

• debugging use cases
• endpoint selection guidance
• payload-size warnings for heavy endpoints
• explanation of wrapper behavior (especially /os/allocation/explain)

3) Fix /os/indices bytes parameter handling

Ensure the bytes query parameter is actually passed through (instead of being hardcoded to mb).

4) Add a small helper for query params (optional but recommended)

Introduce a helper (e.g. _build_query_params) to:

• remove None query params
• serialize booleans as true/false for OpenSearch

Constraints

• Keep endpoints read-only
• Keep existing auth/authorization checks (READ / OPENSEARCH)
• Preserve current OpenSearch TransportError handling pattern
• Keep OpenSearch tag so routes remain exported via MCP

Acceptance Criteria

• New routes are available under the OpenSearch tag
• OpenAPI descriptions are detailed enough for MCP agent usage
• /os/indices?bytes=gb returns values in gb (not always mb)
• No write/mutation OpenSearch routes are added
• opensearch_controller.py passes Python syntax validation