[PGMQ] implement advisory lock when initializing pgmq

Otherwise, concurrent calls to 'IF NOT EXISTS' when creating extension
could result in unique constraint errors.
3 jobs for polymorphic-worker in 9 minutes and 28 seconds (queued for 4 seconds)
Status Job ID Name Coverage
  Build
passed #14065
build

00:03:29

 
  Unit Tests
passed #14066
unit-tests

00:02:36

 
  Integration Tests
failed #14067
integration-tests

00:03:21

 
Name Stage Failure
failed
integration-tests Integration Tests
      can handle a job with timeout (archive strategy):                      OK (14.76s)
can handle a job with timeout (delete strategy): OK (14.50s)
can handle a job with timeout (repeat N times, then archive strategy): OK (20.16s)
can process two jobs: OK (18.02s)
after job with error, continue with another one: OK (14.82s)

2 out of 13 tests failed (20.16s)
Cleaning up project directory and file based variables
ERROR: Job failed: exit code 1