To simplify deployment of the log validator, this allows wildcards
(using go's filepath.Glob) to be included in the file paths.
In order to detect new files, a new background goroutine polls the glob
patterns every minute for matches.
Because the "monitor" function is running in its own goroutine, a lock
is needed to ensure it's not trying to add new tailers while shutdown is
happening.
The main function in log-validator is overly big, so this refactors it
in preparation for adding support for file globs, which is started in
the (currently draft) #7134
This PR should be functionally a no-op, except for one change:
The 1-per-second ratelimiter is moved to be per-file, so it's
1-per-second-per-file. I think this more closely aligns with what we'd
want, as we could potentially miss that a file had bad lines in it if it
was overwhelmed by another log file at the same time.
Matthew McPherrin