compute_ctl: add flag to avoid config step (#4457)

Add backwards-compatible flag that cplane can use to speed up startup time

libs/compute_api/src/spec.rs

@@ -27,6 +27,12 @@ pub struct ComputeSpec {
     pub cluster: Cluster,
     pub delta_operations: Option<Vec<DeltaOp>>,
 
+    /// An optinal hint that can be passed to speed up startup time if we know
+    /// that no pg catalog mutations (like role creation, database creation,
+    /// extension creation) need to be done on the actual database to start.
+    #[serde(default)] // Default false
+    pub skip_pg_catalog_updates: bool,
+
     // Information needed to connect to the storage layer.
     //
     // `tenant_id`, `timeline_id` and `pageserver_connstring` are always needed.