storcon: track pageserver availability zone (#8852)

## Problem
In order to build AZ aware scheduling, the storage controller needs to
know what AZ pageservers are in.

Related https://github.com/neondatabase/neon/issues/8848

## Summary of changes
This patch set adds a new nullable column to the `nodes` table:
`availability_zone_id`. The node registration
request is extended to include the AZ id (pageservers already have this
in their `metadata.json` file).

If the node is already registered, then we update the persistent and
in-memory state with the provided AZ.
Otherwise, we add the node with the AZ to begin with.

A couple assumptions are made here:
1. Pageserver AZ ids are stable
2. AZ ids do not change over time

Once all pageservers have a configured AZ, we can remove the optionals
in the code and make the database column not nullable.

storage_controller/src/node.rs

@@ -36,6 +36,8 @@ pub(crate) struct Node {
     listen_pg_addr: String,
     listen_pg_port: u16,
 
+    availability_zone_id: Option<String>,
+
     // This cancellation token means "stop any RPCs in flight to this node, and don't start
     // any more". It is not related to process shutdown.
     #[serde(skip)]
@@ -61,6 +63,10 @@ impl Node {
         self.id
     }
 
+    pub(crate) fn get_availability_zone_id(&self) -> Option<&str> {
+        self.availability_zone_id.as_deref()
+    }
+
     pub(crate) fn get_scheduling(&self) -> NodeSchedulingPolicy {
         self.scheduling
     }
@@ -72,7 +78,18 @@ impl Node {
     /// Does this registration request match `self`?  This is used when deciding whether a registration
     /// request should be allowed to update an existing record with the same node ID.
     pub(crate) fn registration_match(&self, register_req: &NodeRegisterRequest) -> bool {
-        self.id == register_req.node_id
+        let az_ids_match = {
+            match (
+                self.availability_zone_id.as_deref(),
+                register_req.availability_zone_id.as_deref(),
+            ) {
+                (Some(current_az), Some(register_req_az)) => current_az == register_req_az,
+                _ => true,
+            }
+        };
+
+        az_ids_match
+            && self.id == register_req.node_id
             && self.listen_http_addr == register_req.listen_http_addr
             && self.listen_http_port == register_req.listen_http_port
             && self.listen_pg_addr == register_req.listen_pg_addr
@@ -173,6 +190,7 @@ impl Node {
         listen_http_port: u16,
         listen_pg_addr: String,
         listen_pg_port: u16,
+        availability_zone_id: Option<String>,
     ) -> Self {
         Self {
             id,
@@ -182,6 +200,7 @@ impl Node {
             listen_pg_port,
             scheduling: NodeSchedulingPolicy::Active,
             availability: NodeAvailability::Offline,
+            availability_zone_id,
             cancel: CancellationToken::new(),
         }
     }
@@ -194,6 +213,7 @@ impl Node {
             listen_http_port: self.listen_http_port as i32,
             listen_pg_addr: self.listen_pg_addr.clone(),
             listen_pg_port: self.listen_pg_port as i32,
+            availability_zone_id: self.availability_zone_id.clone(),
         }
     }
 
@@ -208,6 +228,7 @@ impl Node {
             listen_http_port: np.listen_http_port as u16,
             listen_pg_addr: np.listen_pg_addr,
             listen_pg_port: np.listen_pg_port as u16,
+            availability_zone_id: np.availability_zone_id,
             cancel: CancellationToken::new(),
         }
     }