Add is_default field to taxonomy sql models

[allisonking]

Closes https://github.com/ethyca/fides/issues/854

This requires a fideslang update first: https://github.com/ethyca/fideslang/pull/68

Code Changes

• [x] Adds a field is_default to the taxonomy related sql models (DataCategory, DataUse, DataSubject, DataQualifier)
• [x] Alembic migration

Steps to Confirm

• [ ] nox -s dev
• [ ] Check out localhost:8080/docs and open up one of the taxonomy fields (i.e. GET data_category)
• [ ] Should also see the new is_default field in localhost:8080/openapi.json

Pre-Merge Checklist

• [x] All CI Pipelines Succeeded
• Documentation Updated:
  • [ ] documentation complete, or draft/outline provided (tag docs-team to complete/review on this branch)
  • [ ] documentation issue created (tag docs-team to complete issue separately)
• [x] Issue Requirements are Met
• [x] Relevant Follow-Up Issues Created
  • [ ] https://github.com/ethyca/fides/issues/986
  • [ ] https://github.com/ethyca/fides/issues/988
• [x] Update CHANGELOG.md

Description Of Changes

The autogenerated alembic migration looks like it's deleting and recreating indexes. Not sure if that's expected, or if I should just remove those lines?

[allisonking]

Not sure what the docs error is about 😕

[allisonking]

Added this issue to cover preventing users from modifying the default taxonomy https://github.com/ethyca/fides/issues/986

[allisonking]

Bumped fideslang version, should be ready for review now (though docs CI is still failing 😢 )

[allisonking]

whoa never mind, docs build passes now!