Print out the goroutine id (#3433)

The TXT logger prints out the actual go routine ID

This feature depends on 'loggoroutine' build tag

```go build -tags loggoroutine```

formatter/syslog/formatter.go

@@ -0,0 +1,39 @@
+package syslog
+
+import (
+	"fmt"
+	"strings"
+
+	"github.com/sirupsen/logrus"
+
+	"github.com/netbirdio/netbird/formatter/levels"
+)
+
+// Formatter formats logs into text
+type Formatter struct {
+	levelDesc []string
+}
+
+// NewSyslogFormatter create new MySyslogFormatter instance
+func NewSyslogFormatter() *Formatter {
+	return &Formatter{
+		levelDesc: levels.ValidLevelDesc,
+	}
+}
+
+// Format renders a single log entry
+func (f *Formatter) Format(entry *logrus.Entry) ([]byte, error) {
+	var fields string
+	keys := make([]string, 0, len(entry.Data))
+	for k, v := range entry.Data {
+		if k == "source" {
+			continue
+		}
+		keys = append(keys, fmt.Sprintf("%s: %v", k, v))
+	}
+
+	if len(keys) > 0 {
+		fields = fmt.Sprintf("[%s] ", strings.Join(keys, ", "))
+	}
+	return []byte(fmt.Sprintf("%s%s\n", fields, entry.Message)), nil
+}

formatter/syslog/formatter_test.go

@@ -0,0 +1,26 @@
+package syslog
+
+import (
+	"testing"
+	"time"
+
+	"github.com/sirupsen/logrus"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestLogSyslogFormat(t *testing.T) {
+
+	someEntry := &logrus.Entry{
+		Data:    logrus.Fields{"att1": 1, "att2": 2, "source": "some/fancy/path.go:46"},
+		Time:    time.Date(2021, time.Month(2), 21, 1, 10, 30, 0, time.UTC),
+		Level:   3,
+		Message: "Some Message",
+	}
+
+	formatter := NewSyslogFormatter()
+	result, _ := formatter.Format(someEntry)
+
+	parsedString := string(result)
+	expectedString := "^\\[(att1: 1, att2: 2|att2: 2, att1: 1)\\] Some Message\\s+$"
+	assert.Regexp(t, expectedString, parsedString)
+}