MM-22786 enterprise metrics for logging (#15313)

Adds metrics for logging engine which are collected by Prometheus.
- current queue level(s)
- rate of logging records emitted
- rate of logging errors

vendor/github.com/mattermost/logr/target/file.go

@@ -85,8 +85,3 @@ func (f *File) Shutdown(ctx context.Context) error {
 
 	return errs.ErrorOrNil()
 }
-
-// String returns a string representation of this target.
-func (f *File) String() string {
-	return "FileTarget"
-}

vendor/github.com/mattermost/logr/target/syslog.go

@@ -87,8 +87,3 @@ func (s *Syslog) Write(rec *logr.LogRec) error {
 	}
 	return err
 }
-
-// String returns a string representation of this target.
-func (s *Syslog) String() string {
-	return "SyslogTarget"
-}

vendor/github.com/mattermost/logr/target/writer.go

@@ -38,8 +38,3 @@ func (w *Writer) Write(rec *logr.LogRec) error {
 	_, err = w.out.Write(buf.Bytes())
 	return err
 }
-
-// String returns a string representation of this target.
-func (w *Writer) String() string {
-	return "WriterTarget"
-}