feat: new group consistency algorithm

This implements new group consistency algorithm described in
<https://github.com/deltachat/deltachat-core-rust/issues/6401>

New `Chat-Group-Member-Timestamps` header is added
to send timestamps of member additions and removals.
Member is part of the chat if its addition timestamp
is greater or equal to the removal timestamp.

src/securejoin/bob.rs

@@ -59,8 +59,13 @@ pub(super) async fn start_protocol(context: &Context, invite: QrInvite) -> Resul
             // only become usable once the protocol is finished.
             let group_chat_id = state.joining_chat_id(context).await?;
             if !is_contact_in_chat(context, group_chat_id, invite.contact_id()).await? {
-                chat::add_to_chat_contacts_table(context, group_chat_id, &[invite.contact_id()])
-                    .await?;
+                chat::add_to_chat_contacts_table(
+                    context,
+                    time(),
+                    group_chat_id,
+                    &[invite.contact_id()],
+                )
+                .await?;
             }
             let msg = stock_str::secure_join_started(context, invite.contact_id()).await;
             chat::add_info_msg(context, group_chat_id, &msg, time()).await?;