Deprecate APIv2

[humitos]

This is small work-in-progress issue to list what we need to do to deprecate APIv2:

• New dashboard still uses APIv2 due that APIv3 doesn't return all the required fields (API: BuildCommands and missing fields to build v3 API #11179)
• Generic webhooks points to APIv2 (Integrations: generic API incoming webhook uses APIv2 #10760)
• Builders hit APIv2 since APIv3 doesn't support build API key (

  readthedocs.org/readthedocs/core/utils/__init__.py

  Line 166 in 5a4c099

  _, build_api_key = BuildAPIKey.objects.create_key(project=project)

  )