Add OpenMetrics endpoint exposing the basic RPC store metrics as guages

Co-authored-by: Antonio Scandurra <me@as-cii.com>

Cargo.lock

@@ -870,6 +870,7 @@ dependencies = [
  "nanoid",
  "parking_lot 0.11.2",
  "project",
+ "prometheus",
  "rand 0.8.5",
  "reqwest",
  "rpc",
@@ -3401,6 +3402,21 @@ dependencies = [
  "workspace",
 ]
 
+[[package]]
+name = "prometheus"
+version = "0.13.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "cface98dfa6d645ea4c789839f176e4b072265d085bfcc48eaa8d137f58d3c39"
+dependencies = [
+ "cfg-if 1.0.0",
+ "fnv",
+ "lazy_static",
+ "memchr",
+ "parking_lot 0.12.1",
+ "protobuf",
+ "thiserror",
+]
+
 [[package]]
 name = "prost"
 version = "0.8.0"
@@ -3477,6 +3493,12 @@ dependencies = [
  "prost 0.9.0",
 ]
 
+[[package]]
+name = "protobuf"
+version = "2.27.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "cf7e6d18738ecd0902d30d1ad232c9125985a3422929b16c65517b38adc14f96"
+
 [[package]]
 name = "pulldown-cmark"
 version = "0.9.1"