Logging: log time spent to upload build artifacts (#9568)

Start collecting how much time (in seconds) it takes to upload all the build
artifacts for each project.

Related #9448

Author: humitos

readthedocs/projects/tasks/builds.py

@@ -517,6 +517,7 @@ def on_success(self, retval, task_id, args, kwargs):
         pdf = self.data.outcomes['pdf']
         epub = self.data.outcomes['epub']
 
+        time_before_store_build_artifacts = timezone.now()
         # Store build artifacts to storage (local or cloud storage)
         self.store_build_artifacts(
             html=html,
@@ -525,6 +526,10 @@ def on_success(self, retval, task_id, args, kwargs):
             pdf=pdf,
             epub=epub,
         )
+        log.info(
+            "Store build artifacts finished.",
+            time=(timezone.now() - time_before_store_build_artifacts).seconds,
+        )
 
         # NOTE: we are updating the db version instance *only* when
         # HTML are built successfully.