pageserver: add gRPC LSN lease support (#12384)

## Problem

The gRPC API does not provide LSN leases.

## Summary of changes

* Add LSN lease support to the gRPC API.
* Use gRPC LSN leases for static computes with `grpc://` connstrings.
* Move `PageserverProtocol` into the `compute_api::spec` module and
reuse it.

storage_controller/src/compute_hook.rs

@@ -5,7 +5,8 @@ use std::sync::Arc;
 use std::time::Duration;
 
 use anyhow::Context;
-use control_plane::endpoint::{ComputeControlPlane, EndpointStatus, PageserverProtocol};
+use compute_api::spec::PageserverProtocol;
+use control_plane::endpoint::{ComputeControlPlane, EndpointStatus};
 use control_plane::local_env::LocalEnv;
 use futures::StreamExt;
 use hyper::StatusCode;