feat(o11y): add prometheus metrics endpoint and HTTP instrumentation

[pjhampton]

Pull Request Template

Summary

Adds prometheus metrics endpoint

Change Type

Please delete any irrelevant options.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update
• Translation update

Testing

Please describe your test process and include instructions so that we can reproduce your test. If there are any important variables for your testing configuration, list them here.

Start - visit /metrics

1. curl http://localhost:3000/metrics returned default process metrics (CPU, memory, event loop lag, etc.)
2. Made requests to / and /login, then re-curled /metrics -- confirmed both admin_http_requests_total and admin_http_request_duration_seconds appeared with correct labels:

admin_http_requests_total{method="GET",path="/",status_code="200"} 1
admin_http_requests_total{method="GET",path="/login",status_code="307"} 1
admin_http_request_duration_seconds_sum{method="GET",path="/",status_code="200"} 0.162622
admin_http_request_duration_seconds_sum{method="GET",path="/login",status_code="307"} 0.000762375

Test Configuration:

Checklist

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• My code adheres to this project's style guidelines
• I have performed a self-review of my own code
• I have commented in any complex areas of my code
• I have made pertinent documentation changes
• My changes do not introduce new warnings
• I have written tests demonstrating that my changes are effective or that my feature works
• Local unit tests pass with my changes
• Any changes dependent on mine have been merged and published in downstream modules.
• A pull request for updating the documentation has been submitted.

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