[WIP] factor out trace functionality into separate package and add Go docs

replication/driver/replication_driver_test.go

@@ -10,8 +10,8 @@ import (
 	"time"
 
 	"github.com/stretchr/testify/require"
+	"github.com/zrepl/zrepl/daemon/logging/trace"
 
-	"github.com/zrepl/zrepl/daemon/logging"
 	"github.com/zrepl/zrepl/replication/report"
 
 	"github.com/stretchr/testify/assert"
@@ -150,7 +150,7 @@ func (f *mockStep) ReportInfo() *report.StepInfo {
 func TestReplication(t *testing.T) {
 
 	ctx := context.Background()
-	defer logging.WithTaskFromStackUpdateCtx(&ctx)()
+	defer trace.WithTaskFromStackUpdateCtx(&ctx)()
 
 	mp := &mockPlanner{}
 	getReport, wait := Do(ctx, mp)