[C#] feat: AssistantsPlanner file upload and download support

[singhk97]

Linked issues

fixes #1919

Details

• AssistantsPlanner now supports passing in attached files and images within the user message. Files will be uploaded through the OpenAI/Azure OpenAI Files API and the file_id is attached to the message.
• AssistantsPlanner now supports downloading files and images generated in a single run. Only image files are attached to the outgoing activity as a list of Attachments in the PredictedSayCommand default action.

Change details

• Created an AssistantsMessage class that extends ChatMessage. It stores a single MessageContent and files generated with in it in the AttachedFiles property.
• Added a FileClient field to the AssistantsPlanner. It wraps around the Files api.
• Added FileName field in InputFile.cs class. A filename is required to upload a file to Files api.

Samples Updates

• OrderBot is now configured with the file_search tool. A vector store is created, and the menu.pdf file is uploaded to it and the store is attached to the assistant on creation. Users can ask for the menu items or prices and the assistant will be using the file_search tool under the hood to get that information.
• MathBot has no updates - but it can be used to get the assistant to generate a png image of a graph.

Attestation Checklist

• My code follows the style guidelines of this project

• I have checked for/fixed spelling, linting, and other errors

• I have commented my code for clarity

• I have made corresponding changes to the documentation (updating the doc strings in the code is sufficient)

• My changes generate no new warnings

• I have added tests that validates my changes, and provides sufficient test coverage. I have tested with:

  • Local testing
  • E2E testing in Teams

• New and existing unit tests pass locally with my changes

Additional information

Feel free to add other relevant information below