feat: prometheus metrics

Prometheus metrics exposed at /metrics

Cargo.lock

@@ -1207,6 +1207,7 @@ dependencies = [
  "lazy_static",
  "nonzero_ext",
  "parse_duration",
+ "prometheus",
  "r2d2",
  "r2d2_sqlite",
  "rand 0.8.5",
@@ -1545,6 +1546,21 @@ dependencies = [
  "unicode-ident",
 ]
 
+[[package]]
+name = "prometheus"
+version = "0.13.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "449811d15fbdf5ceb5c1144416066429cf82316e2ec8ce0c1f6f8a02e7bbcf8c"
+dependencies = [
+ "cfg-if",
+ "fnv",
+ "lazy_static",
+ "memchr",
+ "parking_lot",
+ "protobuf",
+ "thiserror",
+]
+
 [[package]]
 name = "prost"
 version = "0.11.6"
@@ -1578,6 +1594,12 @@ dependencies = [
  "prost",
 ]
 
+[[package]]
+name = "protobuf"
+version = "2.28.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "106dd99e98437432fed6519dedecfade6a06a73bb7b2a1e019fdd2bee5778d94"
+
 [[package]]
 name = "quanta"
 version = "0.9.3"