feat: Updated docs to reflect behaviour when RD is disabled

Issue: Update docs to document the behaviour of settin... (#432223 - closed)

What does this MR do and why?

Updated the docs to reflect behaviour on UI and API when RD is disabled in the configuration.

How to set up and validate locally

View docs at https://docs.gitlab.com/ee/user/workspace/configuration.html#prerequisites

MR acceptance checklist

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