Backport to 16.5: Geo: Bring back legacy project Prometheus metrics

What does this MR do and why?

Describe in detail what merge request is being backported and why

There was a breaking change that should have gone through deprecation and backward compatibility until a major release. This MR implements backward compatibility of the most important of the affected metrics. This problem has already triggered support tickets, so backporting this fix should reduce ticket volume as more customers upgrade.

#429617 (closed)

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• This MR is backporting a bug fix, documentation update, or spec fix, previously merged in the default branch.
• The MR that fixed the bug on the default branch has been deployed to GitLab.com (not applicable for documentation or spec changes).
• This MR has a severity label assigned (if applicable).
• This MR has been approved by a maintainer (only one approval is required).
• Ensure the e2e:package-and-test-ee job has either succeeded or been approved by a Software Engineer in Test.

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• Refer to the patch release runbook for engineers and maintainers for guidance.
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