Add a capability for receiving sticky events (#157)

In the future when we try to implement the active pushing of the sticky event map to the widget in clients, I believe we will want this to be gated behind a capability. By adding the capability now, we allow widgets to start requesting the capability already and benefit from the improved delivery guarantees of sticky events later for free.

Author: robintown

src/interfaces/Capabilities.ts

@@ -57,6 +57,10 @@ export enum MatrixCapabilities {
      * @experimental It is not recommended to rely on this existing - it can be removed without notice.
      */
     MSC4354SendStickyEvent = "org.matrix.msc4354.send_sticky_event",
+    /**
+     * @experimental It is not recommended to rely on this existing - it can be removed without notice.
+     */
+    MSC4354ReceiveStickyEvent = "org.matrix.msc4354.receive_sticky_event",
 }
 
 export type Capability = MatrixCapabilities | string;