Refactor deprecated operations for OpenAPI

Chance Feickrequested to merge
581045-deprecations-refactor into master

What does this MR do and why?

Refactor deprecated operations for OpenAPI. Follow-up to !214743 (comment 2929573371).

References

How to set up and validate locally

  1. In rails console, generate specification: 
       Rails.application.eager_load!
   api_classes = API::Base.descendants
   entity_classes = Grape::Entity.descendants
   generator = Gitlab::GrapeOpenapi::Generator.new(api_classes: api_classes, entity_classes: entity_classes)
   File.write(Rails.root.join('tmp', 'myfile.json'), generator.generate.to_json)
  2. Use redocly to build documentation: redocly build-docs ~/gdk/gitlab/tmp/myfile.json
  3. Verify deprecations work as expected: e.g. /redoc-static.html#tag/CI-Minutes/operation/postApiV4NamespacesIdMinutes

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Related to #581045 (closed)

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