Implement a second HTTP server within compute_ctl (#10574)

The compute_ctl HTTP server has the following purposes:

- Allow management via the control plane
- Provide an endpoint for scaping metrics
- Provide APIs for compute internal clients
  - Neon Postgres extension for installing remote extensions
  - local_proxy for installing extensions and adding grants

The first two purposes require the HTTP server to be available outside
the compute.

The Neon threat model is a bad actor within our internal network. We
need to reduce the surface area of attack. By exposing unnecessary
unauthenticated HTTP endpoints to the internal network, we increase the
surface area of attack. For endpoints described in the third bullet
point, we can just run an extra HTTP server, which is only bound to the
loopback interface since all consumers of those endpoints are within the
compute.

proxy/src/bin/local_proxy.rs

@@ -85,8 +85,8 @@ struct LocalProxyCliArgs {
     /// Address of the postgres server
     #[clap(long, default_value = "127.0.0.1:5432")]
     postgres: SocketAddr,
-    /// Address of the compute-ctl api service
-    #[clap(long, default_value = "http://127.0.0.1:3080/")]
+    /// Address of the internal compute-ctl api service
+    #[clap(long, default_value = "http://127.0.0.1:3081/")]
     compute_ctl: ApiUrl,
     /// Path of the local proxy config file
     #[clap(long, default_value = "./local_proxy.json")]