presence: Allow bots to fetch realm presence data.

Before, presence information for an entire realm could only be queried via
the `POST /api/v1/users/me/presence` endpoint. However, this endpoint also
updates the presence information for the user making the request. Therefore,
bot users are not allowed to access this endpoint because they don't have
any presence data.

This commit adds a new endpoint `GET /api/v1/realm/presence` that just
returns the presence information for the realm of the caller.

Fixes #10651.

zproject/urls.py

@@ -116,6 +116,9 @@ v1_api_and_json_patterns = [
     url(r'^realm/deactivate$', rest_dispatch,
         {'POST': 'zerver.views.realm.deactivate_realm'}),
 
+    url(r'^realm/presence$', rest_dispatch,
+        {'GET': 'zerver.views.presence.get_statuses_for_realm'}),
+
     # users -> zerver.views.users
     #
     # Since some of these endpoints do something different if used on