Add prysm version to prometheus (#8527)

* Add prysm version to prometheus

* gofmt

* apply suggestion

Co-authored-by: Raul Jordan <raul@prysmaticlabs.com>

shared/version/BUILD.bazel

@@ -2,12 +2,19 @@ load("@prysm//tools/go:def.bzl", "go_library")
 
 go_library(
     name = "go_default_library",
-    srcs = ["version.go"],
+    srcs = [
+        "metrics.go",
+        "version.go",
+    ],
     importpath = "github.com/prysmaticlabs/prysm/shared/version",
     visibility = ["//visibility:public"],
     x_defs = {
         "gitCommit": "{STABLE_GIT_COMMIT}",
         "buildDate": "{DATE}",
         "gitTag": "{STABLE_GIT_TAG}",
     },
+    deps = [
+        "@com_github_prometheus_client_golang//prometheus:go_default_library",
+        "@com_github_prometheus_client_golang//prometheus/promauto:go_default_library",
+    ],
 )

shared/version/metrics.go

@@ -0,0 +1,15 @@
+package version
+
+import (
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/promauto"
+)
+
+var prysmInfo = promauto.NewGauge(prometheus.GaugeOpts{
+	Name:        "prysm_version",
+	ConstLabels: prometheus.Labels{"version": gitTag, "commit": gitCommit},
+})
+
+func init() {
+	prysmInfo.Set(float64(1))
+}