aibridge: proxy observability

[dannykopping]

RFC

Acceptance criteria:

• Requests are logged with appropriate labels
  • Action (proxied to aibridged, passthrough)
    • Passthrough should be debug, proxied info
  • Domain
  • Decrypted (domain was allowlisted)
  • Method
  • Path (not query string params)
  • Provider (if proxied to aibridged)
  • Request ID
• Metrics are present
  • coder_aibridge_proxy_requests_total{proxied=true/false} (counter)
  • coder_aibridge_proxy_errors_total{type=auth/cert/other} (counter)
  • coder_aibridge_proxy_cert_cache_requests_total{hit=true/false} (counter)
  • coder_aibridge_proxy_cert_cache_size (gauge)
  • coder_aibridge_proxy_ttfb_seconds (histogram, "ttfb" = time to first byte; measures the time it takes to read & decrypt request, gives operators insight into proxy performance)
• Has tests