feat: Add tags for identifying platformwide tokens

What does this MR do?

feat: Add tags for identifying platformwide tokens

Adds documentation for tags metadata

Changelog: added <- I'm testing out https://docs.gitlab.com/ee/user/project/changelogs.html#from-the-api

What are the relevant issue numbers?

Does this MR meet the acceptance criteria?

• Changelog entry added
• Documentation created/updated for this project, if necessary
• Tests updated/added for this feature/bug
• Conforms to the code review guidelines
• Conforms to the Go guidelines
• Security reports checked/validated by reviewer