tap_auditor: validate pypi_formula_mappings.json

[cho-m]

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Follow up after #16772 to do schema validation and valid formulae checks.

[Bo98]

Note that json_schemer is a part of the pr_upload gem group so you'll need to add it to audit too. See how rexml is handled in the Gemfile.

[cho-m]

After adding some bad values to JSON, the audit output looks like:

❯ brew audit --tap homebrew/core --only 'json_files,tap_formula_lists'
homebrew/core
  * pypi_formula_mappings.json schema validation failed with following errors:
    * object property at `/aiven-client/foo` is not defined and schema does not allow additional properties
    * value at `/animdl/exclude_packages/1` is not a string
  * pypi_formula_mappings.json references
    formulae or casks that are not found in the homebrew/core tap.
    Invalid formulae or casks: brew
Error: 2 problems in 1 tap detected.

I only created parts of JSON Schema needed to run check, but can choose to fill out the other metadata. I added it to catch things like typos and unwanted empty lists.

Can also consider restricting to homebrew/core if there is any chance external taps may be using JSON in other ways.

[MikeMcQuaid]

@cho-m love the idea!

[cho-m]

Still fine tuning schema. I plan to update homebrew/core side to align normalized names similar to how we name resources.

[cho-m]

This is a simplification of https://packaging.python.org/en/latest/specifications/name-normalization/. It doesn't handle trailing - or consecutive - as those make the regex messier.

[github-actions]

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