feat: Group and broadcast channel descriptions (#7829)

fix https://github.com/chatmail/core/issues/7766

Implementation notes:

- Descriptions are only sent with member additions, when the description
is changed, and when promoting a previously-unpromoted group, in order
not to waste bandwith.
- Descriptions are not loaded everytime a chat object is loaded, because
they are only needed for the profile. Instead, they are in their own
table, and can be loaded with their own JsonRPC call.

---------

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

src/mimefactory.rs

@@ -663,7 +663,7 @@ impl MimeFactory {
 
                 if msg
                     .param
-                    .get_bool(Param::AttachGroupImage)
+                    .get_bool(Param::AttachChatAvatarAndDescription)
                     .unwrap_or_default()
                 {
                     return chat.param.get(Param::ProfileImage).map(Into::into);
@@ -1669,6 +1669,12 @@ impl MimeFactory {
                         mail_builder::headers::text::Text::new(old_name).into(),
                     ));
                 }
+                SystemMessage::GroupDescriptionChanged => {
+                    headers.push((
+                        "Chat-Group-Description-Changed",
+                        mail_builder::headers::text::Text::new("").into(),
+                    ));
+                }
                 SystemMessage::GroupImageChanged => {
                     headers.push((
                         "Chat-Content",
@@ -1683,6 +1689,26 @@ impl MimeFactory {
                 }
                 _ => {}
             }
+
+            if command == SystemMessage::GroupDescriptionChanged
+                || command == SystemMessage::MemberAddedToGroup
+                || msg
+                    .param
+                    .get_bool(Param::AttachChatAvatarAndDescription)
+                    .unwrap_or_default()
+            {
+                let description = chat::get_chat_description(context, chat.id).await?;
+                headers.push((
+                    "Chat-Group-Description",
+                    mail_builder::headers::text::Text::new(description.clone()).into(),
+                ));
+                if let Some(ts) = chat.param.get_i64(Param::GroupDescriptionTimestamp) {
+                    headers.push((
+                        "Chat-Group-Description-Timestamp",
+                        mail_builder::headers::text::Text::new(ts.to_string()).into(),
+                    ));
+                }
+            }
         }
 
         match command {