Update file gitlab_agent_configuration.md
What does this MR do and why?
We had an issue (Update docs to document the behaviour of settin... (#432223 - closed)) and MR (feat: Updated docs to reflect behaviour when RD... (!137560 - merged)) to update the docs for this epic (Allow updating all attributes in agent configur... (&11516 - closed)), but it looks like we only updated the docs for the enabled
attribute, not dns_zone
.
This MR updates the dns_zone docs.