FIX: makes chat user avatar show presence by default (#22490)

It's way more common to have presence enabled than disabled, so we should have been making it the default from start.

This commit also changes the namespace of `<ChatUserAvatar />` into `<Chat::UserAvatar />` and refactors tests.

plugins/chat/test/javascripts/components/chat-channel-title-test.js

@@ -71,7 +71,7 @@ module("Discourse Chat | Component | chat-channel-title", function (hooks) {
     const user = this.channel.chatable.users[0];
 
     assert.true(
-      exists(`.chat-user-avatar-container .avatar[title="${user.username}"]`)
+      exists(`.chat-user-avatar__container .avatar[title="${user.username}"]`)
     );
 
     assert.strictEqual(