Add MSCs to /versions unstable_features

As suggested in matrix-org/matrix-react-sdk#7372 (comment)

Author: MadLittleMods

synapse/config/experimental.py

@@ -32,7 +32,7 @@ def read_config(self, config: JsonDict, **kwargs):
         # MSC3026 (busy presence state)
         self.msc3026_enabled: bool = experimental.get("msc3026_enabled", False)
 
-        # MSC2716 (backfill existing history)
+        # MSC2716 (importing historical messages)
         self.msc2716_enabled: bool = experimental.get("msc2716_enabled", False)
 
         # MSC2285 (hidden read receipts)

synapse/rest/client/versions.py

@@ -93,6 +93,10 @@ def on_GET(self, request: Request) -> Tuple[int, JsonDict]:
                     "org.matrix.msc3026.busy_presence": self.config.experimental.msc3026_enabled,
                     # Supports receiving hidden read receipts as per MSC2285
                     "org.matrix.msc2285": self.config.experimental.msc2285_enabled,
+                    # Adds support for importing historical messages as per MSC2716
+                    "org.matrix.msc2716": self.config.experimental.msc2716_enabled,
+                    # Adds support for jump to date endpoints (/timestamp_to_event) as per MSC3030
+                    "org.matrix.msc3030": self.config.experimental.msc3030_enabled,
                 },
             },
         )