Fixes up PDF summarizer example

[skrawcz]

The request wasn't wired correctly through on the server. When posting files, you have to use the Form object in fastapi if you're also passing in other information.

Also changes DAG to make it clearer to track what the final content passed to the LLM would be.

Changes

• pdf summarizer example

How I tested this

• locally

Notes

Checklist

• PR has an informative and human-readable title (this will be pulled into the release notes)
• Changes are limited to a single goal (no scope creep)
• Code passed the pre-commit check & code is left cleaner/nicer than when first encountered.
• Any change in functionality is tested
• New functions are documented (with a description, list of inputs, and expected output)
• Placeholder code is flagged / future TODOs are captured in comments
• Project documentation has been updated if adding/changing functionality.