Fix the problem that the debug log directory does not exist abnormally

[zc2638]

Fix the problem that the debug log path is set, and the directory does not exist that causes an exception.

cfg.openSinks() will fail because the file Mu does not exist, when run cfg.Build(). ref: https://github.com/uber-go/zap/blob/v1.21.0/config.go#L179

zap's newFileSink method only creates files, not directories automatically. ref: https://github.com/uber-go/zap/blob/v1.21.0/sink.go#L139

[jptosso]

Looks good to me in general, but I'm not sure if it's fine to arbitrarily set the dir mode, maybe we should just generate an error?

I think modsecurity won't create the the directory neither

@fzipi