Add DB Lab notice to logs on SIGKILL to Postgres

Goal

Add DB Lab notice to logs on kill -9. Current logs may be misleading as it easily can be confused with crash.

TODO / How to implement

do $$ raise log 'DB-LAB: ignore the following crash, it is normal, this DB clone is about to be destroyed'; $$; ? а 
do e'begin raise log \' ...text here... \'; end';
do $$begin raise log ' ...text here... '; end$$;

Acceptance criteria