fix: Force djangoapps to be loaded before we run webpack.

In the specific case of webworkers for proctoring, we need to
force Django to load before we run `npm run webpack` so that
the file ../workers.json gets written. See
https://github.com/openedx/edx-proctoring/blob/73c7f55e2be91324fa07fec6e6ac0a667fdd8412/edx_proctoring/apps.py#L46

Also adds JS_ENV_EXTRA_CONFIG, which is required
to create the webworker config.

playbooks/roles/edxapp/templates/edx/bin/edxapp-update-assets.j2

@@ -3,21 +3,24 @@
 export WEBPACK_CONFIG_PATH=webpack.prod.config.js
 export STATIC_ROOT_LMS=/edx/var/edxapp/staticfiles
 export STATIC_ROOT_CMS=/edx/var/edxapp/staticfiles/studio
+export JS_ENV_EXTRA_CONFIG={}
 
 {% if edxapp_staticfiles_storage_overrides %}
 {% for override in edxapp_staticfiles_storage_overrides %}
 export STATICFILES_STORAGE={{ override | quote }}
 sudo -E -H -u {{ edxapp_user }} \
     env "PATH=$PATH" \
-    npm run webpack \
+    {{ edxapp_venv_bin }} python manage.py lms --settings=$EDX_PLATFORM_SETTINGS print_setting STATIC_ROOT WEBPACK_CONFIG_PATH \
+    && npm run webpack \
     && npm run compile-sass -- --theme-dir /edx/var/edx-themes/edx-themes/edx-platform --theme-dir /edx/app/edxapp/edx-platform/themes \
     && {{ edxapp_venv_bin }}/python manage.py lms collectstatic --noinput --settings=$EDX_PLATFORM_SETTINGS \
     && {{ edxapp_venv_bin }}/python manage.py cms collectstatic --noinput --settings=$EDX_PLATFORM_SETTINGS
 {% endfor %}
 {% else %}
 sudo -E -H -u {{ edxapp_user }} \
     env "PATH=$PATH" \
-    npm run webpack \
+    {{ edxapp_venv_bin }} python manage.py lms --settings=$EDX_PLATFORM_SETTINGS print_setting STATIC_ROOT WEBPACK_CONFIG_PATH \
+    && npm run webpack \
     && npm run compile-sass -- --theme-dir /edx/var/edx-themes/edx-themes/edx-platform --theme-dir /edx/app/edxapp/edx-platform/themes \
     && {{ edxapp_venv_bin }}/python manage.py lms collectstatic --noinput --settings=$EDX_PLATFORM_SETTINGS \
     && {{ edxapp_venv_bin }}/python manage.py cms collectstatic --noinput --settings=$EDX_PLATFORM_SETTINGS