log: add --windows-event-log-level to support Windows Event Log

This provides JSON logs in the Windows Event Log.

fs/log.go

@@ -32,6 +32,7 @@ const (
 	LogLevelNotice // Normal logging, -q suppresses
 	LogLevelInfo   // Transfers, needs -v
 	LogLevelDebug  // Debug level, needs -vv
+	LogLevelOff
 )
 
 type logLevelChoices struct{}
@@ -46,6 +47,7 @@ func (logLevelChoices) Choices() []string {
 		LogLevelNotice:    "NOTICE",
 		LogLevelInfo:      "INFO",
 		LogLevelDebug:     "DEBUG",
+		LogLevelOff:       "OFF",
 	}
 }
 
@@ -66,6 +68,7 @@ const (
 	SlogLevelCritical  = slog.Level(12) // More severe than Error
 	SlogLevelAlert     = slog.Level(16) // More severe than Critical
 	SlogLevelEmergency = slog.Level(20) // Most severe
+	SlogLevelOff       = slog.Level(24) // A very high value
 )
 
 // Map our level numbers to slog level numbers
@@ -78,6 +81,7 @@ var levelToSlog = []slog.Level{
 	LogLevelNotice:    SlogLevelNotice,
 	LogLevelInfo:      slog.LevelInfo,
 	LogLevelDebug:     slog.LevelDebug,
+	LogLevelOff:       SlogLevelOff,
 }
 
 // LogValueItem describes keyed item for a JSON log entry