In order to keep all the visitors from all the leads to merge,
the relation between leads and visitors becomes a many2many.
So that after the lead merge, a lead can have multiple visitors.
This commit re-add the page view stat button that were removed
during website_visitor introduction and page tracking refactoring.
This button counts all the pages views from all the visitors linked
tho the current lead. Clicking on it redirect to the complete
navigation history, from all visitors linked to the lead.
Task ID : 2057428
PR #36180