Resolve "API: Environment info missed"

What does this MR do?

Fix environments API documentation filename (was 'enviroments') and link it from API/README.md.

Fix #30156 (closed)

Moving docs to a new location?

• Make sure the old link is not removed and has its contents replaced with a link to the new location.
  • no previous link found in gitlab-ce project (grep -r enviroments)
• Make sure internal links pointing to the document in question are not broken.
  • no previous link found in gitlab-ce project (grep -r enviroments)
• Search and replace any links referring to old docs in GitLab Rails app, specifically under the app/views/ directory.
  • no previous link found in gitlab-ce project (grep -r enviroments)
• If working on CE, submit an MR to EE with the changes as well.