MDEV-26971: JSON file interface to wsrep node state.

Integration with status reporter in wsrep-lib.

Status reporter reports changes in wsrep state and logged errors/
warnings to a json file which then can be read and interpreted by
an external monitoring tool.

Rationale: until the server is fully initialized it is unaccessible
by client and the only source of information is an error log which
is not machine-friendly. Since wsrep node can spend a very long time
in initialization phase (state transfer), it may be a very long time
that automatic tools can't easily monitor its liveness and progression.

New variable: wsrep_status_file specifies the output file name.
If not set, no file is created and no reporting is done.

Reviewed-by: Jan Lindström <jan.lindstrom@mariadb.com>

sql/wsrep_mutex.h

@@ -20,6 +20,7 @@
 #include "wsrep/mutex.hpp"
 
 /* implementation */
+#include "my_global.h"
 #include "my_pthread.h"
 
 class Wsrep_mutex : public wsrep::mutex