Read storage auth token from spec file.

We read the pageserver connection string from the spec file, so let's
read the auth token from the same place.

We've been talking about pre-launching compute nodes that are not
associated with any particular tenant at startup, so that the spec
file is delivered to the compute node later. We cannot change the env
variables after the process has been launched.

We still pass the token to 'postgres' binary in the NEON_AUTH_TOKEN
env variable, but compute_ctl is now responsible for setting it.

compute_tools/src/bin/compute_ctl.rs

@@ -133,6 +133,7 @@ fn main() -> Result<()> {
         .settings
         .find("neon.pageserver_connstring")
         .expect("pageserver connstr should be provided");
+    let storage_auth_token = spec.storage_auth_token.clone();
     let tenant = spec
         .cluster
         .settings
@@ -153,6 +154,7 @@ fn main() -> Result<()> {
         tenant,
         timeline,
         pageserver_connstr,
+        storage_auth_token,
         metrics: ComputeMetrics::default(),
         state: RwLock::new(ComputeState::new()),
     };