This commit adds a `MiniSchedulerLongRunningJobLogger` class which will
poll every 60 seconds for mini_scheduler jobs which are stuck. When it
detects that a job is stuck, it will log a warning message with the
current backtrace of the thread that is executing the job.
Note that for scheduled jobs which are executed at a frequency of less
than 30 minutes, we will log when the job has been executing for 30
minutes.
For scheduled jobs executed at a frequency of less than 2 hours, we will
log when the job has been executing for a duration greater than its
specified frequency.
For scheduled jobs executed at a frequency greater than 2 hours, we will
log as long as the job has been executing for more than 2 hours.
Alan Guo Xiang Tan