Replica - stop assuming every plugin supports publications

Pulpcore no longer assumes that every plugin which implements support
for the Replication feature supports publications (e.g. container
doesn't).

closes #5464

(cherry picked from commit 37e076b)

CHANGES/5464.bugfix

@@ -0,0 +1,2 @@
+Pulpcore no longer assumes that every plugin implementing the Replication feature supports
+Publications.

pulpcore/app/replica.py

@@ -99,7 +99,9 @@ def remote_extra_fields(self, upstream_distribution):
         return {}
 
     def create_or_update_remote(self, upstream_distribution):
-        if not upstream_distribution["repository"] and not upstream_distribution["publication"]:
+        if not upstream_distribution.get("repository") and not upstream_distribution.get(
+            "publication"
+        ):
             return None
         url = self.url(upstream_distribution)
         remote_fields_dict = {"url": url}