[IMP] bus: notify user when assets have changed

Use case:
When the server is restarted, the python is updated,
but some users may have an ongoing session in a browser tab
This may lead to code being unsynchronized and ultimately to some
odd bugs.

Purpose:
When we are in such a case, that is, the assets were recomputed
after a update of the code and a restart of the server by the request of another user,
notify connected users that assets have changed.
Then propose them to reload the page.

Known caveats:
- This is not a developer's feature.
Since assets computing is ORM cached, they have limited
opportunities to rebuild. Namely, the feature won't trigger
each time the JS has changed, rather, it will
when JS has changed AND the cache has been reset somehow (e.g. when the server is restarted).

- This not a portal/website feature either, but only in backend.
Business clients won't be notified that the JS has changed.

- While requests debug=assets do trigger a recomputing
of the *components* of bundles, they do not save a bundle
This means that the requests that sends the notification
cannot be debug=assets.

Task 2034462

closes odoo/odoo#39875

Signed-off-by: Mathieu Duckerts-Antoine <Polymorphe57@users.noreply.github.com>