notify adding reactions (#6072)

this PR adds an event for reactions received for one's own messages.

this will allow UIs to add notification for these reactions.

**Screenshots** at https://github.com/deltachat/deltachat-ios/pull/2331:

---------

Co-authored-by: iequidoo <117991069+iequidoo@users.noreply.github.com>

src/receive_imf.rs

@@ -1473,6 +1473,7 @@ async fn add_parts(
     for part in &mime_parser.parts {
         if part.is_reaction {
             let reaction_str = simplify::remove_footers(part.msg.as_str());
+            let is_incoming_fresh = mime_parser.incoming && !seen && !fetching_existing_messages;
             set_msg_reaction(
                 context,
                 mime_in_reply_to,
@@ -1480,6 +1481,7 @@ async fn add_parts(
                 from_id,
                 sort_timestamp,
                 Reaction::from(reaction_str.as_str()),
+                is_incoming_fresh,
             )
             .await?;
         }