FF cleanup: Only allow documented token types for GraphQL authentication

What does this MR do and why?

Only allow documented token types for GraphQL authentication. Cleans up graphql_minimal_auth_methods feature flag introduced in !150407 (merged)

Rollout issue: https://gitlab.com/gitlab-org/gitlab/-/issues/444929

MR acceptance checklist

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Before	After

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

1. Set up a project locally with git lfs
2. Get an LFS token via the ssh interface: ssh -p 2222 git@<LOCAL_HOSTNAME> git-lfs-authenticate <NAMESPACE>/<PROJECT_NAME>.git download
3. Copy the token from the "header":{"Authorization":"Basic <COPY_THIS_TOKEN> section
4. Make a GraphQL request to http(s)://<HOSTNAME>:<PORT>/api/graphql.git using the token in the Authorization: Basic <COPIED_TOKEN> header:
   curl -X "POST" "http://localhost:3000/api/graphql.git" -H 'Content-Type: application/json; charset=utf-8' -u 'USERNAME:COPIED_TOKEN' -d $'{"query": "query{currentUser{id username}}","variables": {}}'
5. The request should no longer be authenticated; currentUser should return null and restricted resources should not be accessible.