Pre-install anon extension from compute_ctl

if anon is in shared_preload_libraries.
Users cannot install it themselves, because superuser is required.

GRANT all priveleged needed to use it to db_owner

We use the neon fork of the extension, because small change to sql file
is needed to allow db_owner to use it.

This feature is behind a feature flag AnonExtension,
so it is not enabled by default.

libs/compute_api/src/spec.rs

@@ -90,6 +90,9 @@ pub enum ComputeFeature {
     /// track short-lived connections as user activity.
     ActivityMonitorExperimental,
 
+    /// Pre-install and initialize anon extension for every database in the cluster
+    AnonExtension,
+
     /// This is a special feature flag that is used to represent unknown feature flags.
     /// Basically all unknown to enum flags are represented as this one. See unit test
     /// `parse_unknown_features()` for more details.