Add support for remote extensions. When requested, downloads a tar.gz file for the extension and then organizes the contained files. For instance, placing .so files in sharelib.

libs/compute_api/src/responses.rs

@@ -75,6 +75,7 @@ pub struct ComputeMetrics {
     pub start_postgres_ms: u64,
     pub config_ms: u64,
     pub total_startup_ms: u64,
+    pub load_libraries_ms: u64,
 }
 
 /// Response of the `/computes/{compute_id}/spec` control-plane API.

libs/compute_api/src/spec.rs

@@ -60,6 +60,9 @@ pub struct ComputeSpec {
     /// If set, 'storage_auth_token' is used as the password to authenticate to
     /// the pageserver and safekeepers.
     pub storage_auth_token: Option<String>,
+
+    // list of prefixes to search for custom extensions in remote extension storage
+    pub custom_extensions: Option<Vec<String>>,
 }
 
 #[serde_as]