feat(tvix/nar-bridge): wire up metrics layer

This provides some global HTTP statistics.

Change-Id: I8bd3e034123154a49d94720b0c8d0c3babde5ae3
Reviewed-on: https://cl.tvl.fyi/c/depot/+/12557
Reviewed-by: Jonas Chevalier <zimbatm@zimbatm.com>
Tested-by: BuildkiteCI
Reviewed-by: flokli <flokli@flokli.de>

tvix/Cargo.lock

@@ -2196,6 +2196,7 @@ dependencies = [
  "lru",
  "mimalloc",
  "nix-compat",
+ "opentelemetry",
  "parking_lot",
  "prost",
  "prost-build",
@@ -2209,6 +2210,7 @@ dependencies = [
  "tonic-build",
  "tower 0.4.13",
  "tower-http",
+ "tower-otel-http-metrics",
  "tracing",
  "tracing-subscriber",
  "tvix-castore",
@@ -4369,6 +4371,21 @@ version = "0.3.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "121c2a6cda46980bb0fcd1647ffaf6cd3fc79a013de288782836f6df9c48780e"
 
+[[package]]
+name = "tower-otel-http-metrics"
+version = "0.8.0"
+source = "git+https://github.com/francoposa/tower-otel-http-metrics?rev=2023a58e7287a691872f8e75f433179d29d1b439#2023a58e7287a691872f8e75f433179d29d1b439"
+dependencies = [
+ "futures-core",
+ "futures-util",
+ "http",
+ "opentelemetry",
+ "pin-project-lite",
+ "tower 0.5.1",
+ "tower-layer",
+ "tower-service",
+]
+
 [[package]]
 name = "tower-service"
 version = "0.3.3"