Admin Token API: Add support for reading OAuth Application Secrets

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What does this MR do and why?

This MR adds support for OAuth application secrets to the Admin Token API.

Issue: #443597 (closed)

🛠️ with ❤️ at Siemens

References

• 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. You'll need to create two new tokens:

   1. A personal access token with admin_mode and api capabilities.
   2. An oauth application secret that you can query.

2. Now you can retrieve information about this token:

curl -k --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": "gloas-token-from-step-1-2"}'

Related to #443597 (closed)