[FIX] website: allow user to create/remove website.menu

Before this commit, an user could not create or remove a website.menu since
there was no list/form view for it. Changing sequence also impossible.
Therefore, it was impossible to create or delete a menu from an event. (you
could just edit the existing one)

Now, user can access in debug mode to the list and form view of website.menu to
manage the menus.

This commit also add a link on the ir.ui.view form view to access it's related
website.page

This closes #21302