[ENH] Add endpoint that returns term ID-label mappings for vocab of a given attribute (nb:Assessment)

[alyssadai]

Closes #197

Changes proposed in this pull request:

• New API path created under /attributes router: /attributes/{data_element_URI}/vocab
  • New response model created for this endpoint which includes info about the vocab namespace and the term-label mappings as a dict
  • {data_element_URI} validated as enum to flag unrecognized CDEs
• Workflow to fetch raw vocab implemented for Cognitive Atlas (i.e., when data_element_URI=="nb:Assessment")
  • Involves startup events that will:
    1. Attempt to request the raw cogatlas JSON blob using their API
    2. If a. fails, emit a warning and default to a backup JSON dump of the vocab stored in the repo
• Tests added for new startup events and response from new endpoint

Checklist

• PR has an interpretable title with a prefix ([ENH], [FIX], [REF], [TST], [CI], [MNT], [INF], [MODEL], [DOC]) (see https://neurobagel.org/contributing/pull_requests for more info)
• PR links to GitHub issue with mention Closes #XXXX
• Tests pass
• Checks pass

For new features:

• Tests have been added

For bug fixes:

• There is at least one test that would fail under the original bug conditions.

[coveralls]

Pull Request Test Coverage Report for Build 6565245867

• 113 of 113 (100.0%) changed or added relevant lines in 6 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.04%) to 99.826%

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Totals
Change from base Build 6474650526:	0.04%
Covered Lines:	575
Relevant Lines:	576

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💛 - Coveralls

[surchs]

Thanks for this impressive PR @alyssadai. This took me a second to work through because it is complex, mostly necessarily, I think. I did leave a couple of comments where I think we can make the code clearer or provide context for the future.

Since this is the cogatlas / assessment tool endpoint, I'd also update the PR title to reflect that.

Take a look, apply what you agree with - everything works so after that: 🧑‍🍳