Document what metadata fields go into nwb and update tests

When doing hotfix #63, realized there is no documentation in the repo on what exact aind metadata fields should go into the nwb. When tracing the commit history, seems like information from the procedures json was being used but then it was removed because it was causing problems.

I believe there is a sharepoint document or spreadsheet with this information somewhere, so we should add it as documentation here since this a core library used in many of the pipelines so it's documented and versioned. This will also help in updating tests and catching regressions (I thought I had fixed #63 earlier but because tests didn't scope it, it fell through), and will allow for more scoped tests to make sure the correct metadata is landing in the nwb (I think right now only the session description is being tested so we can add more).

The issue names no files or tests. Start by tracing the commit history around hotfix #63 and locating where procedures JSON metadata was used or removed. Use the available SharePoint document or spreadsheet to define the exact AIND metadata fields for NWB, then document them in the repository and add scoped tests that verify those fields, beyond the existing session-description coverage.

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