Allow to join an open group

Also:

* Refactor interacting with a remote event so that you can interact with
  a remote group as well
* Add a setting for group admins to pick between an open and invite-only
  group
* Fix new groups without posts/todos/resources/events/conversations URL
  set
* Repair local groups that haven't got their
  posts/todos/resources/events/conversations URL set
* Add a scheduled job to refresh remote groups every hour
* Add a user setting to pick when to receive notifications when there's
  new members to approve (will be used when this feature is available)
* Fix pagination for members

Signed-off-by: Thomas Citharel <tcit@tcit.fr>

js/src/graphql/event.ts

@@ -574,3 +574,35 @@ export const EVENT_PERSON_PARTICIPATION_SUBSCRIPTION_CHANGED = gql`
     }
   }
 `;
+
+export const GROUP_MEMBERSHIP_SUBSCRIPTION_CHANGED = gql`
+  subscription($actorId: ID!) {
+    groupMembershipChanged(personId: $actorId) {
+      id
+      memberships {
+        total
+        elements {
+          id
+          role
+          parent {
+            id
+            preferredUsername
+            name
+            domain
+            avatar {
+              id
+              url
+            }
+          }
+          invitedBy {
+            id
+            preferredUsername
+            name
+          }
+          insertedAt
+          updatedAt
+        }
+      }
+    }
+  }
+`;