Register sliding sync under a different path (#17331)

As the API is slightly incompatible.

changelog.d/17331.misc

@@ -0,0 +1 @@
+Change path of the experimental [MSC3575](https://github.com/matrix-org/matrix-spec-proposals/pull/3575) Sliding Sync implementation to `/org.matrix.simplified_msc3575/sync` since our simplified API is slightly incompatible with what's in the current MSC.

synapse/rest/client/sync.py

@@ -864,7 +864,7 @@ class SlidingSyncRestServlet(RestServlet):
     """
 
     PATTERNS = client_patterns(
-        "/org.matrix.msc3575/sync$", releases=[], v1=False, unstable=True
+        "/org.matrix.simplified_msc3575/sync$", releases=[], v1=False, unstable=True
     )
 
     def __init__(self, hs: "HomeServer"):

tests/rest/client/test_sync.py

@@ -1228,7 +1228,9 @@ class SlidingSyncTestCase(unittest.HomeserverTestCase):
 
     def prepare(self, reactor: MemoryReactor, clock: Clock, hs: HomeServer) -> None:
         self.store = hs.get_datastores().main
-        self.sync_endpoint = "/_matrix/client/unstable/org.matrix.msc3575/sync"
+        self.sync_endpoint = (
+            "/_matrix/client/unstable/org.matrix.simplified_msc3575/sync"
+        )
         self.store = hs.get_datastores().main
         self.event_sources = hs.get_event_sources()