These may be redefined to customize log rotation path prefixes,
including use of a directory. File extensions are still up to
individual log writers to add themselves during the actual rotation.
These new also allow for some simplication to the default
ASCII postprocessor function: it eliminates the need for it doing an
extra/awkward rename() operation that only changes the timestamp format.
This also teaches the supervisor framework to use these new options
to rotate ascii logs into a log-queue/ directory with a specific
file name format (intended for an external archiver process to
monitor separately).
This helps prevent a node from being killed/crashing in the middle
of writing a log, restarting, and eventually clobbering that log
file that never underwent the rotation/archival process.
The old `archive-log` and `post-terminate` scripts as used by
ZeekControl previously implemented this behavior, but the new logic is
entirely in the ASCII writer. It uses ".shadow" log files stored
alongside the real log to help detect such scenarios and rotate them
correctly upon the next startup of the Zeek process.
