This commit fixes multiple bugs when serving a `website.page` which has a
trailing slash:
1. We use a 301 instead of a 302 as it is done for every other dispatching
flows (mostly through the redirect in `_postprocess_args()`)
2. The language is no more lost during the dispatching, before this commit
`/fr_BE/contactus/` would redirect to `/contactus`
3. The URL params are no more lost during the dispatching, before this commit
`/contactus/?a=b` would redirect to `/contactus`
opw-2505818
opw-2513575
Community: https://github.com/odoo/odoo/pull/71065
Enterprise: https://github.com/odoo/enterprise/pull/18615