Document API v1/v2 availability on CircleCI Server (SUPENG-552)

[denislemire]

Summary

• Adds a Guides page that compares API v1.1 and v2 availability on CircleCI Server 4.7, 4.8, 4.9, and 4.10 with Cloud.
• Replaces the hostname-only Server API note so readers are not told that swapping circleci.com is enough.
• Links the page from the API intro, developers guide, API homepage, and Server 4.7–4.10 FAQs.

The Cloud OpenAPI reference remains the schema source. This page covers Cloud-only paths, version gates, working endpoint families, and Server admin v1. It does not enumerate every OpenAPI operationId.

Test plan

• Vale: confirm ci/circleci: lint is green on the new and changed .adoc files
• Preview the build artifact and check table scroll on the new page
• Follow xrefs from API intro, developers guide, API homepage, and a Server FAQ
• On-prem review of the 4.7 vs 4.8+ status columns (project create, settings, usage export, pipeline definitions)

[linear-code]

SUPENG-552

[rosieyohannan]

This looks like a great idea. I would love to get the server version support "tags" or something into the API reference docs too. Could use this list as a reference to do that if it's fully verified

[denislemire]

This was verified from code as source of truth so it should be pretty accurate.

I actually meant to talk to you about this PR to see if you had any thoughts on how to best structure this info… Docs on API availability are a bit lacking, this PR was triggered by a ticket from one of our Server customers.

Also looking to strike the right balance of customers being able to find what does / doesn't exist without exposing too much unnecessary information and/or internals… The PR probably still needs a bit more work in that regard.