Admin Token API: Revoke token

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What does this MR do and why?

This commit adds an admin API for token revocation.

Adds a REST API that allows the following:

DELETE /api/v4/admin/token

Attribute	Type	Required	Description
token	string	Yes	Token that should be revoked.

Issue: #499958 (closed)

🛠️ with ❤️ at Siemens

MR acceptance checklist

MR Checklist ( @nwittstruck)

• Changelog entry added, if necessary
• Documentation created/updated via this MR
• Documentation reviewed by technical writer or follow-up review issue created
• Tests added for this feature/bug
• Tested in all supported browsers
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the javascript style guides
• Conforms to the database guides

How to set up and validate locally

1. Enable both feature flags via rails c:

Feature.enable(:admin_agnostic_token_finder)
Feature.enable(:api_admin_token_revoke)

2. You'll need to create two new personal access tokens: https://gdk.test:3443/-/user_settings/personal_access_tokens

   1. A personal access token with admin capabilities.
   2. A personal access token with limited capabilities that you want to revoke. You can also revoke the admin token if you'd like, however for testing I prefer to use separate tokens.

3. Now you can revoke a token:

curl -k --request DELETE \
--url 'https://gdk.test:3443/api/v4/admin/token \       
--header 'Authorization: Bearer <Admin Token from Step 1.>' \
--header 'Content-Type: application/json' \
--data '{"token": "glpat-<example-token-from-step-2>"}'

Related to #499958 (closed)