Update dependency prometheus to v3

Summary

The Prometheus v3 major release is now available, let's proceed with full validation and upgrade to it.

Acceptance criteria

• Upgrade Prometheus to v3

Proposal validation

This is a major version upgrade. I think we should test this within the context of everything we provide as part of https://docs.gitlab.com/ee/administration/monitoring/prometheus/, including:

• Custom scrape metrics instructions.
• Setting up Standalone Prometheus on multi node setup.
• Fresh install.
• Upgrading from previous version with custom data pre-setup.
• Verifying our example queries still work.
• Verify Grafana set up instructions are still up-to-date
• Verify exporters operate properly.