[FIX] website_event_track: PWA install & ServiceWorker caching

This PR aims at preventing the cluttering of the ServiceWorker's cache by filtering out non-necessary assets and preventing "opaque" responses from being cached.

Also, it registers earlier the listener for the PWA install event, allowing to properly show the installation's banner in most of the case.

Finally, it fixes the optional URL's language parsing by allowing custom language naming.

closes odoo/odoo#58994

Signed-off-by: Adrien Dieudonné (adr) <adr@odoo.com>