feat: add OpenTelemetry HTTP client instrumentation

Add otelhttp transport to HTTP client for automatic distributed tracing
of all outbound HTTP requests. This enables better observability and
tracing of GitHub API calls.

Author: d0ugal

go.mod

@@ -7,6 +7,7 @@ toolchain go1.25.3
 require (
 	github.com/d0ugal/promexporter v1.7.1
 	github.com/prometheus/client_golang v1.23.2
+	go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp v0.63.0
 	go.opentelemetry.io/otel v1.38.0
 	gopkg.in/yaml.v3 v3.0.1
 )
@@ -19,6 +20,7 @@ require (
 	github.com/cenkalti/backoff/v5 v5.0.3 // indirect
 	github.com/cespare/xxhash/v2 v2.3.0 // indirect
 	github.com/cloudwego/base64x v0.1.6 // indirect
+	github.com/felixge/httpsnoop v1.0.4 // indirect
 	github.com/gabriel-vasile/mimetype v1.4.11 // indirect
 	github.com/gin-contrib/sse v1.1.0 // indirect
 	github.com/gin-gonic/gin v1.11.0 // indirect

go.sum

@@ -17,6 +17,8 @@ github.com/d0ugal/promexporter v1.7.1/go.mod h1:p0n8/4FE6X0P05tWWicjxHh0lXq9h4qs
 github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
 github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/felixge/httpsnoop v1.0.4 h1:NFTV2Zj1bL4mc9sqWACXbQFVBBg2W3GPvqp8/ESS2Wg=
+github.com/felixge/httpsnoop v1.0.4/go.mod h1:m8KPJKqk1gH5J9DgRY2ASl2lWCfGKXixSwevea8zH2U=
 github.com/gabriel-vasile/mimetype v1.4.11 h1:AQvxbp830wPhHTqc1u7nzoLT+ZFxGY7emj5DR5DYFik=
 github.com/gabriel-vasile/mimetype v1.4.11/go.mod h1:d+9Oxyo1wTzWdyVUPMmXFvp4F9tea18J8ufA774AB3s=
 github.com/gin-contrib/sse v1.1.0 h1:n0w2GMuUpWDVp7qSpvze6fAu9iRxJY4Hmj6AmBOU05w=
@@ -107,6 +109,8 @@ github.com/ugorji/go/codec v1.3.1 h1:waO7eEiFDwidsBN6agj1vJQ4AG7lh2yqXyOXqhgQuyY
 github.com/ugorji/go/codec v1.3.1/go.mod h1:pRBVtBSKl77K30Bv8R2P+cLSGaTtex6fsA2Wjqmfxj4=
 go.opentelemetry.io/auto/sdk v1.2.1 h1:jXsnJ4Lmnqd11kwkBV2LgLoFMZKizbCi5fNZ/ipaZ64=
 go.opentelemetry.io/auto/sdk v1.2.1/go.mod h1:KRTj+aOaElaLi+wW1kO/DZRXwkF4C5xPbEe3ZiIhN7Y=
+go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp v0.63.0 h1:RbKq8BG0FI8OiXhBfcRtqqHcZcka+gU3cskNuf05R18=
+go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp v0.63.0/go.mod h1:h06DGIukJOevXaj/xrNjhi/2098RZzcLTbc0jDAUbsg=
 go.opentelemetry.io/otel v1.38.0 h1:RkfdswUDRimDg0m2Az18RKOsnI8UDzppJAtj01/Ymk8=
 go.opentelemetry.io/otel v1.38.0/go.mod h1:zcmtmQ1+YmQM9wrNsTGV/q/uyusom3P8RxwExxkZhjM=
 go.opentelemetry.io/otel/exporters/otlp/otlptrace v1.38.0 h1:GqRJVj7UmLjCVyVJ3ZFLdPRmhDUp2zFmQe3RHIOsw24=

internal/collectors/ghcr_collector.go

@@ -17,6 +17,7 @@ import (
 	"github.com/d0ugal/promexporter/app"
 	"github.com/d0ugal/promexporter/tracing"
 	"github.com/prometheus/client_golang/prometheus"
+	"go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp"
 	"go.opentelemetry.io/otel/attribute"
 )
 
@@ -79,7 +80,8 @@ func NewGHCRCollector(cfg *config.Config, registry *metrics.GHCRRegistry, app *a
 		metrics: registry,
 		app:     app,
 		client: &http.Client{
-			Timeout: 30 * time.Second,
+			Timeout:   30 * time.Second,
+			Transport: otelhttp.NewTransport(http.DefaultTransport),
 		},
 		token: cfg.GitHub.Token.Value(),
 	}