Prevent non-superusers from reading pg_backend_memory_contexts, by default.

 Prevent non-superusers from reading pg_backend_memory_contexts, by default.
 
 pg_backend_memory_contexts view contains some internal information of
 memory contexts. Since exposing them to any users by default may cause
 security issue, this commit allows only superusers to read this view,
 by default, like we do for pg_shmem_allocations view.
 
 Bump catalog version.
 
 Author: Atsushi Torikoshi
 Reviewed-by: Michael Paquier, Fujii Masao
 Discussion: https://postgr.es/m/1414992.1597849297@sss.pgh.pa.us