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

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

src/bot/load_config.rs

@@ -35,6 +35,9 @@ pub fn load() -> anyhow::Result<Config> {
             }
             cfg_env::BAIBOT_USER_NAME => config.user.name = value,
             cfg_env::BAIBOT_COMMAND_PREFIX => config.command_prefix = value,
+            cfg_env::BAIBOT_ROOM_POST_JOIN_SELF_INTRODUCTION_ENABLED => {
+                config.room.post_join_self_introduction_enabled = value.parse::<bool>()?;
+            }
             cfg_env::BAIBOT_LOGGING => {
                 config.logging = value;
             }