Add config setting controlling if a self-introduction message is posted after joining a room

Fixes https://github.com/etkecc/baibot/issues/32

src/controller/join/mod.rs

@@ -8,6 +8,12 @@ pub async fn handle(
     room: &mxlink::matrix_sdk::Room,
     room_config_context: &RoomConfigContext,
 ) -> anyhow::Result<()> {
+    if !bot.post_join_self_introduction_enabled() {
+        tracing::debug!("Post-join self-introduction is disabled - not sending introduction message");
+
+        return Ok(());
+    }
+
     let agent_manager = bot.agent_manager();
 
     bot.messaging()