rtla/tests: Test timerlat -P option using actions

rtla/tests: Test timerlat -P option using actions

The -P option is used to set priority of osnoise and timerlat threads.

Extend the test for -P with --on-threshold calling a script that looks
for running timerlat threads and checks if their priority is set
correctly.

As --on-threshold is only supported by timerlat at the moment, this is
only implemented there so far.

Cc: John Kacur <jkacur@redhat.com>
Cc: Luis Goncalves <lgoncalv@redhat.com>
Cc: Chang Yin <cyin@redhat.com>
Cc: Costa Shulyupin <costa.shul@redhat.com>
Link: https://lore.kernel.org/20250725133817.59237-3-tglozar@redhat.com
Signed-off-by: Tomas Glozar <tglozar@redhat.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>