feat: Make gossip period configurable (#4346)

This is needed to test periodic re-gossiping in existing chats.

Also add a test for verified groups on that even if "member added" message is missed by a device of
newly added member, after re-gossiping Autocrypt keys to the group it successfully learns these keys
and marks other members as verified.

src/config.rs

@@ -318,6 +318,13 @@ pub enum Config {
 
     /// Last message processed by the bot.
     LastMsgId,
+
+    /// How often to gossip Autocrypt keys in chats with multiple recipients, in seconds. 2 days by
+    /// default.
+    ///
+    /// This is not supposed to be changed by UIs and only used for testing.
+    #[strum(props(default = "172800"))]
+    GossipPeriod,
 }
 
 impl Context {

src/context.rs

@@ -754,7 +754,6 @@ impl Context {
                 .await?
                 .to_string(),
         );
-
         res.insert(
             "debug_logging",
             self.get_config_int(Config::DebugLogging).await?.to_string(),
@@ -763,6 +762,10 @@ impl Context {
             "last_msg_id",
             self.get_config_int(Config::LastMsgId).await?.to_string(),
         );
+        res.insert(
+            "gossip_period",
+            self.get_config_int(Config::GossipPeriod).await?.to_string(),
+        );
 
         let elapsed = self.creation_time.elapsed();
         res.insert("uptime", duration_to_str(elapsed.unwrap_or_default()));

src/mimefactory.rs

@@ -359,9 +359,10 @@ impl<'a> MimeFactory<'a> {
     async fn should_do_gossip(&self, context: &Context) -> Result<bool> {
         match &self.loaded {
             Loaded::Message { chat } => {
-                // beside key- and member-changes, force re-gossip every 48 hours
+                // beside key- and member-changes, force a periodic re-gossip.
                 let gossiped_timestamp = chat.id.get_gossiped_timestamp(context).await?;
-                if time() > gossiped_timestamp + (2 * 24 * 60 * 60) {
+                let gossip_period = context.get_config_i64(Config::GossipPeriod).await?;
+                if time() >= gossiped_timestamp + gossip_period {
                     Ok(true)
                 } else {
                     let cmd = self.msg.param.get_cmd();