Add Category loading from YAML source with validation

[danielpgross]

Similar to #443, but for categories: this PR adds the ability to load Category objects from a YAML source with validation.

This implementation fully supports secondary paths to a given category defined using a secondary_children key in the YAML source containing an array. Example:

- id: aa
  name: Apparel & Accessories
  children:
  - aa-1
  attributes:
  - color
- id: aa-1
  name: Clothing
  children: []
  secondary_children:
  - bi-19-10
- id: bi
  name: Business & Industrial
  children:
  - bi-19
  attributes:
  - color
- id: bi-19
  name: Medical
  children:
  - bi-19-10
  attributes:
  - color
- id: bi-19-10
  name: Scrubs
  children: []
  attributes:
  - color

The approach to loading categories is also different from the prototype: load_from_source takes the parsed YAML objects for all verticals (not just one). This was needed because:

• We need to be able to resolve secondary paths, which can run through a different vertical
• We need to check uniqueness across all verticals

[danielpgross]

Warning

This pull request is not mergeable via GitHub because a downstack PR is open. Once all requirements are satisfied, merge this PR as a stack on Graphite.
Learn more

• Add Category loading from YAML source with validation #449 👈 (View in Graphite)
• Refactor ModelIndex to use hashes instead of sets #450
• main

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[graphite-app]

The ancestors array is being built in the wrong order. The current code returns ancestors from child to root, but the tests expect root to child order. Change to parent.ancestors + [parent] to match test expectations.

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[danielpgross]

This one's not correct, the tests expect child to root order. (This line was copied from the existing code to keep existing behaviour.)

[elsom25]

I assume usage of this will come in later PRs?

[danielpgross]

For now I've been using it for debugging, ex. for recursively printing out the taxonomy

[elsom25]

🙌