cloud/bmaas/bmdb: implement BMDB client metrics

This implements some basic BMDB metrics exported by any client code
using the BMDB.

It also enables their use in the Shepherd and BMSRV.

Change-Id: I1d5e82fd2c34a7bfd42f37fad540d69f7b23f347
Reviewed-on: https://review.monogon.dev/c/monogon/+/1600
Tested-by: Jenkins CI
Reviewed-by: Tim Windelschmidt <tim@monogon.tech>
diff --git a/cloud/bmaas/bmdb/metrics/BUILD.bazel b/cloud/bmaas/bmdb/metrics/BUILD.bazel
new file mode 100644
index 0000000..d5eb8a5
--- /dev/null
+++ b/cloud/bmaas/bmdb/metrics/BUILD.bazel
@@ -0,0 +1,12 @@
+load("@io_bazel_rules_go//go:def.bzl", "go_library")
+
+go_library(
+    name = "metrics",
+    srcs = ["metrics.go"],
+    importpath = "source.monogon.dev/cloud/bmaas/bmdb/metrics",
+    visibility = ["//visibility:public"],
+    deps = [
+        "//cloud/bmaas/bmdb/model",
+        "@com_github_prometheus_client_golang//prometheus",
+    ],
+)