storage controller: include stripe size in compute notifications (#6974)

## Problem

- The storage controller is the source of truth for a tenant's stripe
size, but doesn't currently have a way to propagate that to compute:
we're just using the default stripe size everywhere.

Closes: https://github.com/neondatabase/neon/issues/6903

## Summary of changes

- Include stripe size in `ComputeHookNotifyRequest`
- Include stripe size in `LocationConfigResponse`

The stripe size is optional: it will only be advertised for
multi-sharded tenants. This enables the controller to defer the choice
of stripe size until we split a tenant for the first time.

control_plane/src/bin/neon_local.rs

@@ -1024,7 +1024,7 @@ async fn handle_endpoint(ep_match: &ArgMatches, env: &local_env::LocalEnv) -> Re
                         })
                         .collect::<Vec<_>>()
                 };
-            endpoint.reconfigure(pageservers).await?;
+            endpoint.reconfigure(pageservers, None).await?;
         }
         "stop" => {
             let endpoint_id = sub_args

control_plane/src/endpoint.rs

@@ -52,6 +52,7 @@ use compute_api::spec::RemoteExtSpec;
 use compute_api::spec::Role;
 use nix::sys::signal::kill;
 use nix::sys::signal::Signal;
+use pageserver_api::shard::ShardStripeSize;
 use serde::{Deserialize, Serialize};
 use url::Host;
 use utils::id::{NodeId, TenantId, TimelineId};
@@ -735,7 +736,11 @@ impl Endpoint {
         }
     }
 
-    pub async fn reconfigure(&self, mut pageservers: Vec<(Host, u16)>) -> Result<()> {
+    pub async fn reconfigure(
+        &self,
+        mut pageservers: Vec<(Host, u16)>,
+        stripe_size: Option<ShardStripeSize>,
+    ) -> Result<()> {
         let mut spec: ComputeSpec = {
             let spec_path = self.endpoint_path().join("spec.json");
             let file = std::fs::File::open(spec_path)?;
@@ -765,6 +770,9 @@ impl Endpoint {
         let pageserver_connstr = Self::build_pageserver_connstr(&pageservers);
         assert!(!pageserver_connstr.is_empty());
         spec.pageserver_connstring = Some(pageserver_connstr);
+        if stripe_size.is_some() {
+            spec.shard_stripe_size = stripe_size.map(|s| s.0 as usize);
+        }
 
         let client = reqwest::Client::new();
         let response = client