feat: Check other endpoints for ATAC artifacts

[ivirshup]

Reason for Change

• Verify GET /v1/collections/{collection_id}/datasets/{dataset_id} and GET /v1/datasets return the fragment and index artifacts. single-cell#741

Changes

• added FRAGMENT_INDEX artifact type
• modified permanent url resolution code to account for URI for fragment indices
• added tests checking that atac artifacts are returned by the API

Notes for reviewer

In the specification doc there is some inconsistency around what the index artifact is called. I went with FRAGMENT_INDEX but FRAGMENT_TABIX is also used in the spec.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

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Additional details and impacted files

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##             feature/schema-5-3    #7442   +/-   ##
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  Hits                          ?    15550           
  Misses                        ?     1171           
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unittests	92.99% <100.00%> (?)

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[Bento007]

A few minor things to fix

[Bento007]

We landed on using ATAC_FRAGMENT, and ATAC_INDEX