Explore::ProjectsController should tolerate single Gitaly node failure

This issue is one piece of #33616 (closed), which was part of a production incident.

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If a single Gitaly node fails in some critical way (cannot be reset, rebooted, removed, etc), and you have repositories on that server, you will experience 500 errors when rendering bits of pages that need access to that data.

This controller includes /explore, /explore/projects/trending, /explore/projects, and /explore/projects/starred.

A related issue (#34722 (closed)) identified that this endpoint is making a license call that is potentially causing this. Work was also done to default the avatar icon and remove the CI status if they are not available.