[Refactor] Complete metrics overhaul

Metrics got an entire overhaul. Instead of relying on a broken
prometheus library to publish our metrics, we now use the
`tracing` library and with OpenTelemetry that we bind together
then publish into a prometheus library.

Metrics are now mostly derive-macros. This means that the struct
can express what it wants to export and a help text. The library
will choose if it is able to export it.

Tracing now works by calling `.publish()` on the parent structs,
those structs need to call `.publish()` on all the child members
it wishes to publish data about. If a "group" is requested, use
the `group!()` macro, which under-the-hood calls `tracing::span`
with some special labels. At primitive layers, it will call the
`publish!()` macro, which will call `tracing::event!()` macro
under-the-hood with some special fields set. A custom
`tracing::Subscriber` will intercept all the events and spans
and convert them into a json-like object. This object can then
be exported as real json or encoded into other formats like
otel/prometheus.

closes: #1164, #650, #384, #209
towards: #206

BUILD.bazel

@@ -16,6 +16,8 @@ rust_binary(
     deps = [
         "//nativelink-config",
         "//nativelink-error",
+        "//nativelink-metric",
+        "//nativelink-metric-collector",
         "//nativelink-proto",
         "//nativelink-scheduler",
         "//nativelink-service",
@@ -28,16 +30,22 @@ rust_binary(
         "@crates//:futures",
         "@crates//:hyper",
         "@crates//:mimalloc",
+        "@crates//:opentelemetry",
+        "@crates//:opentelemetry-prometheus",
+        "@crates//:opentelemetry_sdk",
         "@crates//:parking_lot",
+        "@crates//:prometheus",
         "@crates//:prometheus-client",
         "@crates//:rustls-pemfile",
         "@crates//:scopeguard",
+        "@crates//:serde_json",
         "@crates//:serde_json5",
         "@crates//:tokio",
         "@crates//:tokio-rustls",
         "@crates//:tonic",
         "@crates//:tower",
         "@crates//:tracing",
+        "@crates//:tracing-subscriber",
     ],
 )