feat: otel go metrics setup

[tim-mwangi]

Description

Set up otel go metrics reporting and add a RequestCount metric for the http handler instrumentation. This should enable metrics to be created and exported just like spans are. By default we will export to the otlp endpoint spans are exported to but this can be overridden using a metrics endpoint config.

Testing

Tested locally.

Checklist:

• [ ✅ ] My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• [✅ ] Any dependent changes have been merged and published in downstream modules

[codecov]

Codecov Report

Merging #200 (1cebe35) into main (c886e58) will increase coverage by 0.53%.
The diff coverage is 76.69%.

@@            Coverage Diff             @@
##             main     #200      +/-   ##
==========================================
+ Coverage   64.99%   65.52%   +0.53%     
==========================================
  Files          49       49              
  Lines        1774     1868      +94     
==========================================
+ Hits         1153     1224      +71     
- Misses        570      587      +17     
- Partials       51       57       +6     

Impacted Files	Coverage Δ
...nstrumentation/hypertrace/net/hyperhttp/handler.go	0.00% <0.00%> (ø)
instrumentation/opentelemetry/init.go	80.06% <72.60%> (-2.45%)	⬇️
sdk/instrumentation/net/http/handler.go	28.69% <84.21%> (+2.84%)	⬆️
...nstrumentation/opencensus/net/hyperhttp/handler.go	100.00% <100.00%> (ø)
...opentelemetry/github.com/gin-gonic/hypergin/gin.go	89.36% <100.00%> (+0.23%)	⬆️
...n/opentelemetry/github.com/gorilla/hypermux/mux.go	65.21% <100.00%> (+1.58%)	⬆️
...rumentation/opentelemetry/net/hyperhttp/handler.go	100.00% <100.00%> (ø)

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[tim-mwangi]

I need to move this otel specific logic out of the sdk since this is meant to be a hypertrace sdk that can be adapted by any telemetry framework. But can do that separately.

[ryanericson]

This means if metrics backend is down instrumented app won't be able to start? Better to fail silently?

[tim-mwangi]

If the metrics/traces collector is down and you bring up the go app with this agent in it, it comes up without issue. You do get context deadline messages since you cannot export anything. After you bring up the collector the spans and metrics start being sent.