storcon: provide an az id in metadata.json from neon local (#8897)

## Problem
Neon local set-up does not inject an az id in `metadata.json`. See real
change in https://github.com/neondatabase/neon/pull/8852.

## Summary of changes
We piggyback on the existing `availability_zone` pageserver
configuration in order to avoid making neon local even more complex.

control_plane/src/pageserver.rs

@@ -181,6 +181,23 @@ impl PageServerNode {
         );
         io::stdout().flush()?;
 
+        // If the config file we got as a CLI argument includes the `availability_zone`
+        // config, then use that to populate the `metadata.json` file for the pageserver.
+        // In production the deployment orchestrator does this for us.
+        let az_id = conf
+            .other
+            .get("availability_zone")
+            .map(|toml| {
+                let az_str = toml.to_string();
+                // Trim the (") chars from the toml representation
+                if az_str.starts_with('"') && az_str.ends_with('"') {
+                    az_str[1..az_str.len() - 1].to_string()
+                } else {
+                    az_str
+                }
+            })
+            .unwrap_or("local".to_string());
+
         let config = self
             .pageserver_init_make_toml(conf)
             .context("make pageserver toml")?;
@@ -216,6 +233,7 @@ impl PageServerNode {
         let (_http_host, http_port) =
             parse_host_port(&self.conf.listen_http_addr).expect("Unable to parse listen_http_addr");
         let http_port = http_port.unwrap_or(9898);
+
         // Intentionally hand-craft JSON: this acts as an implicit format compat test
         // in case the pageserver-side structure is edited, and reflects the real life
         // situation: the metadata is written by some other script.
@@ -226,7 +244,10 @@ impl PageServerNode {
                 postgres_port: self.pg_connection_config.port(),
                 http_host: "localhost".to_string(),
                 http_port,
-                other: HashMap::new(),
+                other: HashMap::from([(
+                    "availability_zone_id".to_string(),
+                    serde_json::json!(az_id),
+                )]),
             })
             .unwrap(),
         )