Summary

Mirage is deprecated and as part of the decommissioning work we need to notify customers that some endpoints will be sunset in the coming months. This PR adds an api deprecation note for the impacted endpoints.

Documentation checklist

• [No changelog entry] Is there a changelog entry (guidelines)? If you don't add one for something awesome and new (however small) — how will our customers find out? Changelogs are automatically posted to RSS feeds, the Discord, and X.
• The change adheres to the documentation style guide.
• If a larger change - such as adding a new page- an issue has been opened in relation to any incorrect or out of date information that this PR fixes.
• Files which have changed name or location have been allocated redirects.