Update Runner registry and cache documentation page
What does this MR do?
- Change the document title
- Adds an overview section to the page that summarizes the configuration options to consider.
- Add the GitLab Dependency Proxy option as the first entry after the overview.
Why was this MR needed?
The Runner registry_and_cache_servers install documentation page does not include the GitLab Dependency Proxy as an option
What are the relevant issue numbers?
Edited by Steve Xuereb