Use randomly generated conference names for Jitsi

Fixes https://github.com/vector-im/element-web/issues/15205
Replaces https://github.com/matrix-org/matrix-react-sdk/pull/5322

This change uses a random ID for the Jitsi conference name to avoid any badly-named Jitsi calls, and overrides the "subject" (title) of the call so end users aren't typically exposed to the random ID.

src/utils/WidgetUtils.ts

@@ -477,6 +477,7 @@ export default class WidgetUtils {
             'userId=$matrix_user_id',
             'roomId=$matrix_room_id',
             'theme=$theme',
+            'roomName=$roomName',
         ];
         if (opts.auth) {
             queryStringParts.push(`auth=${opts.auth}`);