Tweak documentation for saltutils.find_cached_job.
Tweak documentation for saltutils.find_cached_job.

This function only works if the minion is configured with cache_jobs set to
True. Explicitly documenting this will make it less likely that users will
be confused when it silently fails to work for them.

Fixes #27735.

saltstack/salt,saltstack/salt,saltstack/salt,saltstack/salt,saltstack/salt