Add Feed Tokens to Token information API

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What does this MR do and why?

Due to the refactoring of the token identification, the Token information API can now handle feed tokens.

This commit adds a spec and updates the documentation.

🛠 with ❤ at Siemens

References

• MR that added the support for feed tokens
• Issue
• Docs for Token Information API

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 feature flag via rails c:

Feature.enable(:admin_agnostic_token_finder)

2. You'll need to create a personal access token and retrieve your feed token:

   1. Create a personal access token with admin capabilities.
   2. Create a feed token to query.

3. Now you can retrieve information about this token:

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

{
	"id": 1,
	"username": "root",
	"name": "Administrator",
	"state": "active",
	...
}

Related to #443597 (closed)