extend DBMS_MONITOR (or at least DBMS_SYSTEM.set_ev) to allow setting dbk*/dbg* based tracing

DBMS_MONITOR and DBMS_SYSTEM.set_ev seems to be built around the KSD (Kernel Service Debug) infrastructure.

It would be more convenient having an PL/SQL interface to dbk*/dbg* debug functions.

the current method vie ALTER [SESSION|SYSTEM] set events '....' is quite error prone.