Removes logrus package and refactors logging messages (#5293)

This fix removes logrus package dependency and refactors the console
logging as the only logging mechanism by removing file logging support.
It rearranges the log message format and adds stack trace information
whenever trace information is not available in the error structure.
It also adds `--json` flag support for server logging.
When minio server is started with `--json` flag, all log messages are
displayed in json format, with no start-up and informational log
messages.
Fixes #5265 #5220 #5197

cmd/config-versions.go

@@ -418,6 +418,21 @@ type serverConfigV15 struct {
 	Notify *notifier `json:"notify"`
 }
 
+// FileLogger is introduced to workaround the dependency about logrus
+type FileLogger struct {
+	Enable   bool   `json:"enable"`
+	Filename string `json:"filename"`
+}
+
+// ConsoleLogger is introduced to workaround the dependency about logrus
+type ConsoleLogger struct {
+	Enable bool `json:"enable"`
+}
+
+// Loggers struct is defined with FileLogger and ConsoleLogger
+// although they are removed from logging logic. They are
+// kept here just to workaround the dependency migration
+// code/logic has on them.
 type loggers struct {
 	sync.RWMutex
 	Console ConsoleLogger `json:"console"`