Add Supervisor::{stdout,stderr}_hook

These allow capturing/handling the stdout/stderr of child processes
via Zeek scripts.

scripts/base/frameworks/supervisor/api.zeek

@@ -117,4 +117,28 @@ export {
 	##          It's an error to call this function from a process other than
 	##          a supervised one.
 	global node: function(): NodeConfig;
+
+	## Hooks intercepted stdout stream for all supervisor's child processes.
+	##
+	## node: the name of a previously created node via
+	##       :zeek:see:`Supervisor::create` indicating to which
+	##       child process the stdout line is associated.
+	##       An empty value is used to indicate the message
+	##       came from the internal supervisor stem process
+	##       (this should typically never happen).
+	##
+	## msg: line-buffered contents from the stdout of a child process.
+	global stdout_hook: hook(node: string, msg: string);
+
+	## Hooks intercepted stderr stream for all supervisor's child processes.
+	##
+	## node: the name of a previously created node via
+	##       :zeek:see:`Supervisor::create` indicating to which
+	##       child process the stdout line is associated.
+	##       A empty value is used to indicate the message
+	##       came from the internal supervisor stem process.
+	##       (this should typically never happen).
+	##
+	## msg: line-buffered contents from the stderr of a child process.
+	global stderr_hook: hook(node: string, msg: string);
 }