[Agentic Search] Improve integration with memory / tracing

[ohltyler]

Some upcoming features, such as memory_id being passed in the agentic query clause, and a new search response processor for returning the agent tracing/thinking via ext field, can be leveraged on the UI in a few places:

• new optional field in the search query to include a memory ID for conversational search use cases
• new default search pipeline with the new search response processor, in conjunction with the currently-preset agentic_query_translator search request processor.
• new tab in the search response to show the ext field with the agent response (if applicable)