logging/ascii: Support leftover log rotation in non-supervisor setups

We have a use case to rotate leftover log files in a non-supervisor
setup. There doesn't seem to be a strict requirement on supervisor
functionality. Allow enabling leftover log rotation through
LogAscii::enable_leftover_log_rotation and redef this for the
logger node in a supervisor setup individually.

scripts/base/frameworks/cluster/nodes/logger.zeek

@@ -37,6 +37,8 @@ function supervisor_rotation_format_func(ri: Log::RotationFmtInfo): Log::Rotatio
 
 redef Log::rotation_format_func = supervisor_rotation_format_func;
 
+redef LogAscii::enable_leftover_log_rotation = T;
+
 @else
 
 ## Use the cluster's archive logging script.

scripts/base/frameworks/logging/writers/ascii.zeek

@@ -26,6 +26,12 @@ export {
 	## This option is also available as a per-filter ``$config`` option.
 	const use_json = F &redef;
 
+	## If true, enable leftover log rotation using .shadow files.
+	##
+	## This requires a positive rotation_interval to be configued
+	## to have an effect.
+	const enable_leftover_log_rotation = F &redef;
+
 	## If true, valid UTF-8 sequences will pass through unescaped and be
 	## written into logs.
 	##