chatapi: assistants file search tool (fixes #8533)

[Mutugiii]

Fixes #8533

Using the file search tool for assistants to upload and use context from files.

To test pull the relevant container:

docker pull treehouses/planet-tags:0.18.17-8533-chatapi-text-extraction-to-file-search-a99af8fa
docker pull treehouses/planet-tags:chatapi-0.18.17-8533-chatapi-text-extraction-to-file-search-a99af8fa

Can be tested with a course step that has a file -> So far tested with pdf and docx.

In the future, need to gracefully handle errors for limitations(in particular for file sizes) https://platform.openai.com/docs/guides/tools-file-search#limitations