[REF] bus,website_livechat: import bus frontend assets in bus instead of website_livechat

This commit moves the import of bus JS files in the frontend assets from
website_livechat to the bus module itself.

This is done in preparation of the "survey live mode" feature that will also
require the bus files in the frontend context.

PR #43568
Task 1972640

addons/bus/views/bus.xml

@@ -8,6 +8,14 @@
         </xpath>
     </template>
 
+    <template id="assets_frontend" name="im assets" inherit_id="web.assets_frontend">
+        <xpath expr="." position="inside">
+            <script type="text/javascript" src="/bus/static/src/js/longpolling_bus.js"></script>
+            <script type="text/javascript" src="/bus/static/src/js/crosstab_bus.js"></script>
+            <script type="text/javascript" src="/bus/static/src/js/services/bus_service.js"></script>
+        </xpath>
+    </template>
+
     <template id="qunit_suite" name="bus tests" inherit_id="web.qunit_suite">
         <xpath expr="//script[last()]" position="after">
             <script type="text/javascript" src="/bus/static/tests/bus_tests.js"/>

addons/website_livechat/views/website_livechat.xml

@@ -20,10 +20,6 @@
                     <script type="text/javascript" src="/mail/static/src/js/thread_windows/abstract_thread_window.js"></script>
                     <script type="text/javascript" src="/im_livechat/static/src/js/website_livechat_window.js"></script>
 
-                <script type="text/javascript" src="/bus/static/src/js/longpolling_bus.js"></script>
-                <script type="text/javascript" src="/bus/static/src/js/crosstab_bus.js"></script>
-                <script type="text/javascript" src="/bus/static/src/js/services/bus_service.js"></script>
-
                 <script type="text/javascript" src="/mail/static/src/js/document_viewer.js"></script>
                 <script type="text/javascript" src="/mail/static/src/js/thread_widget.js"></script>
                 <script type="text/javascript" src="/mail/static/src/js/utils.js"></script>