Pass context to event publishing.

To allow tracing propagation via events, we need to pass the context
to the `Publish` function of reva events. This adds the context
everywhere where events are published. If there was no context to pass,
we started a new one with `context.Background()`.

services/postprocessing/pkg/service/service.go

@@ -1,6 +1,7 @@
 package service
 
 import (
+	"context"
 	"encoding/json"
 	"fmt"
 
@@ -88,7 +89,7 @@ func (pps *PostprocessingService) Run() error {
 			pp, err = getPP(pps.store, ev.UploadID)
 			if err != nil {
 				if err == store.ErrNotFound {
-					if err := events.Publish(pps.pub, events.RestartPostprocessing{
+					if err := events.Publish(context.Background(), pps.pub, events.RestartPostprocessing{
 						UploadID:  ev.UploadID,
 						Timestamp: ev.Timestamp,
 					}); err != nil {
@@ -109,7 +110,7 @@ func (pps *PostprocessingService) Run() error {
 			}
 		}
 		if next != nil {
-			if err := events.Publish(pps.pub, next); err != nil {
+			if err := events.Publish(context.Background(), pps.pub, next); err != nil {
 				pps.log.Error().Err(err).Msg("unable to publish event")
 				return err // we can't publish -> we are screwed
 			}