Add stable unstable version for jump to date before v1.6 is fully sup…

…ported on Synapse

Related to #15089

Element Web PR to honor `org.matrix.msc3030.stable`: matrix-org/matrix-react-sdk#10398

synapse/rest/client/versions.py

@@ -111,6 +111,10 @@ def on_GET(self, request: Request) -> Tuple[int, JsonDict]:
                     "fi.mau.msc2815": self.config.experimental.msc2815_enabled,
                     # Adds a ping endpoint for appservices to check HS->AS connection
                     "fi.mau.msc2659": self.config.experimental.msc2659_enabled,
+                    # Adds support for jump to date endpoints (/timestamp_to_event) as per MSC3030.
+                    # TODO: Remove when Synapse advertises support for `v1.6` which includes MSC3030
+                    # (https://github.com/matrix-org/synapse/issues/15089)
+                    "org.matrix.msc3030.stable": True,
                     # Adds support for login token requests as per MSC3882
                     "org.matrix.msc3882": self.config.experimental.msc3882_enabled,
                     # Adds support for remotely enabling/disabling pushers, as per MSC3881