Sanitize custom_stages and stages_enabled

[timolegros]

Link to Issue

Closes: #6718

Description of Changes

• Updated Community.stages_enabled column type from string to boolean
  • This includes converting all undefined and empty string values to false in the DB
• Updated Community.custom_stages column type from string to array of strings
  • This includes converting all improperly formatted stringified arrays into proper arrays in the DB
• Updated the API to only accept and return an array for custom_stages

Test Plan

Requires FLAG_NEW_ADMIN_ONBOARDING=true to be set. Also requires a fresh database dump (yarn dump-db).

• Run yarn db-all
• Enable/Disable stages
• Create stages like ['test 123', 'test 321'] and ["test one", "test two"]
• Remove custom stages after creation

Other Considerations

The migration includes queries that convert custom_stages to an array of strings for specific communities. This is because there is no easy/clean generalized approach for converting these values. It is important to note that should these values change for the community before this migration is run, the migration may fail. That said, the client currently in production already includes validation for 99% of cases. There are 2 ways an incorrect value could be inserted:

1. A user accesses the API directly and provides a faulty value
2. A user defines a list on the client with single quotes instead of double quotes (client-side validation does not cover this case until this PR is merged).

[mzparacha]

LGTM

[lzach83]

LGTM

[CowMuon]

Approved for Common release v. 1.0 (nee v0.9.6)