[Observability] Add metrics export to PEAS

[commoddity]

Objective

Add the ability to export metrics to Prometheus and Grafana to PEAS to add observability to our production dashboards.

Origin Document

Discord chat: https://discord.com/channels/824324475256438814/1263851886486880356/1372914921720905770

We need observability on auth requests and rate limiter headers to allow better understanding of auth reqeust processing.

Goals

• Export key metrics to our observability stack (eg. processing latency, auth failures & reasons, etc.)

Deliverables

• Add functionality to export metrics

• Add specific metrics at key points in the code (likely all can be added to auth_handler.go and other key files in auth package.

• Comments: Add/update TODOs and comments alongside the source code so it is easier to follow.

• Testing: Add new tests (unit and/or E2E) to the test suite.

• Makefile: Add new targets to the Makefile to make the new functionality easier to use.

• Documentation: Update architectural or development READMEs; use mermaid diagrams where appropriate.

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Creator: @commoddity
Co-Owners: @adshmh @Olshansk