Add storage_broker binary.

Which ought to replace etcd. This patch only adds the binary and adjusts
Dockerfile to include it; subsequent ones will add deploy of helm chart and the
actual replacement.

It is a simple and fast pub-sub message bus. In this patch only safekeeper
message is supported, but others can be easily added.

Compilation now requires protoc to be installed. Installing protobuf-compiler
package is fine for Debian/Ubuntu.

ref
https://github.com/neondatabase/neon/pull/2733
https://github.com/neondatabase/neon/issues/2394

storage_broker/Cargo.toml

@@ -0,0 +1,37 @@
+[package]
+name = "storage_broker"
+version = "0.1.0"
+edition = "2021"
+
+[features]
+bench = []
+
+[dependencies]
+async-stream = "0.3"
+bytes = "1.0"
+clap = { version = "4.0", features = ["derive"] }
+futures = "0.3"
+futures-core = "0.3"
+futures-util = "0.3"
+git-version = "0.3.5"
+humantime = "2.1.0"
+hyper = {version = "0.14.14", features = ["full"]}
+once_cell = "1.13.0"
+parking_lot = "0.12"
+prost = "0.11"
+tonic = "0.8"
+tokio = { version = "1.0", features = ["macros", "rt-multi-thread"] }
+tokio-stream = "0.1"
+tracing = "0.1.27"
+
+metrics = { path = "../libs/metrics" }
+utils = { path = "../libs/utils" }
+workspace_hack = { version = "0.1", path = "../workspace_hack" }
+
+[build-dependencies]
+tonic-build = "0.8"
+
+[[bench]]
+name = "rps"
+harness = false
+