Ee 25990 interactive web terminals for ci cd jobs docs

What does this MR do?

Documents the interactive web terminal feature for EE

Related issues

gitlab-org/gitlab-ce#25990

Releated merge requests

gitlab-org/gitlab-ce!20719

Moving docs to a new location?

Read the guidelines: https://docs.gitlab.com/ee/development/documentation/#changing-document-location

• Make sure the old link is not removed and has its contents replaced with a link to the new location.
• Make sure internal links pointing to the document in question are not broken.
• Search and replace any links referring to the old docs in the GitLab Rails app, specifically under the app/views/ and ee/app/views (for GitLab EE) directories.
• Make sure to add redirect_from to the new document if there are any Disqus comments on the old document thread.
• If working on CE and the ee-compat-check jobs fails, submit an MR to EE with the changes as well.
• Ping one of the technical writers for review.