limit using verison in extension creation to admin user for all extensions
by using supautils and before-create hooks
add test for this in pg_net

For pg_net background worker, we need to switch the version of the
extension on the file system (both pg_net.so and pg_net.control need to point
to the desired version).

As the extension is in the Nix store, we cannot simply symlink to the
desired version, as the Nix store is read-only. 
To work around this, we use overlayfs to create a writable layer on top
of the pg_net store path.

This reverts commit 268cadb.

This reverts commit 4996d81.

This change would not resolve the issue it was targeting.