sql: implement pg_my_temp_schema and pg_is_other_temp_schema

Exalate commented:


https://github.com/cockroachdb/cockroach/pull/69909 --- Release note (sql change): The pg_is_other_temp_schema builtin function is now supported, which returns whether the given OID is the OID of another session's temporary schema.  Release justification: None, waiting for v22.1.

Jira Issue: DOC-1721