Enable the recommendation bot to search for specific resource details

[mbertrand]

What are the relevant tickets?

Closes https://github.com/mitodl/hq/issues/6542

Description (What does it do?)

• Adds the search_content_files tool to the list of tools available to the recommendation bot, and tweaks the system prompt to provide guidance on when to use it.
• Adjusts the summarization node/function to work more appropriately (noticed some issues during testing, since the trigger to use it was hit more often due to the greater # of tokens used up by the content files tool).

How can this be tested?

Ask for course recommendations, then ask for some detailed info about 1 or more of the courses (how is it graded, are there any class projects, etc). Keep the conversation going for awhile to ensure the summarization is hit, responses seem reasonable, and no exceptions occur.

Additional Context

I needed to make some changes to the summarization code, because it assumed one tool call at a time, and after a couple rounds of summarization led to some tool output messages getting truncated from the list of messages sent to the summarization llm, leading to exceptions. As part of fixing that, I also simplified it a bit and forced it to create a summary only if the final message is a human message, to fully prevent any occurrences of human input -> tool call -> summarization -> response which often led to subpar responses compared to human input -> summarization -> tool call -> response.