Add MSC2716 and MSC3030 to `/versions` -> `unstable_features` (#11582)

As suggested in https://github.com/matrix-org/matrix-react-sdk/pull/7372#discussion_r769523369

changelog.d/11582.misc

+Add [MSC2716](https://github.com/matrix-org/matrix-doc/pull/2716) and [MSC3030](https://github.com/matrix-org/matrix-doc/pull/3030) to `/versions` -> `unstable_features` to detect server support.

synapse/config/experimental.py

@@ -32,7 +32,7 @@ class ExperimentalConfig(Config):
         # 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 @@ class VersionsRestServlet(RestServlet):
                     "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,
                 },
             },
         )