When we create internal tables in citus_internal, a regular user cannot
really do that because they can't access citus_internal. Even if we
switch to extension owner, we will need to switch while also dropping
tables etc, which is not trivial and clear.
Hence cimv_internal schema is created and the owner of the CIMV will own
the tables in this schema, hence only they can access those tables.
Relname itself is not unique across the database hence for internal CIMV
related tables we use a unique id prefix instead of just relname
so that the same mv in two different schemas don't cause overlap.