Expose Prometheus metrics

[ibetitsmike]

Required:

• all partitioned by provider, model, client, user_id, endpoint, streaming (where applicable)
• all the metrics collected in the telemetry packet
• interception_duration
• passthrough count -> partitioned by provider, endpoint, user_id

We'll import the prometheus client in aibridge
coder/coder will pass in registerer, wrap with labels / name prefix

i.e.
aibridge_interception_duration
-> coderd_aibridge_interception_duration

[dannykopping]

This will slip this release unfortunately.