jsonrpc: add is_broadcast property

to `ChatListItemFetchResult`

CHANGELOG.md

@@ -11,6 +11,7 @@
   and `dc_event_emitter_unref()` should be used instead of
   `dc_accounts_event_emitter_unref`.
 - add `dc_contact_was_seen_recently()` #3560
+- jsonrpc: add `is_broadcast` property to `ChatListItemFetchResult`
 
 ### Changes
 - order contact lists by "last seen";