add helper function to register/listen/serve prometheus metrics. (#10)

Signed-off-by: Kenny Leung <kleung@chainguard.dev>

go.mod

@@ -3,15 +3,39 @@ module chainguard.dev/go-grpc-kit
 go 1.17
 
 require (
+	github.com/grpc-ecosystem/go-grpc-prometheus v1.2.0
 	github.com/grpc-ecosystem/grpc-gateway/v2 v2.7.3
-	golang.org/x/net v0.0.0-20220127200216-cd36cc0744dd
+	github.com/prometheus/client_golang v1.11.1
+	golang.org/x/net v0.0.0-20220225172249-27dd8689420f
 	google.golang.org/grpc v1.44.0
+	knative.dev/pkg v0.0.0-20220705130606-e60d250dc637
 )
 
 require (
+	github.com/beorn7/perks v1.0.1 // indirect
+	github.com/cespare/xxhash/v2 v2.1.1 // indirect
+	github.com/go-logr/logr v1.2.2 // indirect
+	github.com/gogo/protobuf v1.3.2 // indirect
 	github.com/golang/protobuf v1.5.2 // indirect
-	golang.org/x/sys v0.0.0-20211216021012-1d35b9e2eb4e // indirect
+	github.com/google/go-cmp v0.5.7 // indirect
+	github.com/google/gofuzz v1.2.0 // indirect
+	github.com/json-iterator/go v1.1.12 // indirect
+	github.com/matttproud/golang_protobuf_extensions v1.0.2-0.20181231171920-c182affec369 // indirect
+	github.com/modern-go/concurrent v0.0.0-20180306012644-bacd9c7ef1dd // indirect
+	github.com/modern-go/reflect2 v1.0.2 // indirect
+	github.com/prometheus/client_model v0.2.0 // indirect
+	github.com/prometheus/common v0.32.1 // indirect
+	github.com/prometheus/procfs v0.6.0 // indirect
+	golang.org/x/sys v0.0.0-20220227234510-4e6760a101f9 // indirect
 	golang.org/x/text v0.3.7 // indirect
 	google.golang.org/genproto v0.0.0-20220118154757-00ab72f36ad5 // indirect
 	google.golang.org/protobuf v1.27.1 // indirect
+	gopkg.in/inf.v0 v0.9.1 // indirect
+	gopkg.in/yaml.v2 v2.4.0 // indirect
+	k8s.io/api v0.23.8 // indirect
+	k8s.io/apimachinery v0.23.8 // indirect
+	k8s.io/klog/v2 v2.60.1-0.20220317184644-43cc75f9ae89 // indirect
+	k8s.io/utils v0.0.0-20220210201930-3a6ce19ff2f9 // indirect
+	sigs.k8s.io/json v0.0.0-20211020170558-c049b76a60c6 // indirect
+	sigs.k8s.io/structured-merge-diff/v4 v4.2.1 // indirect
 )