*: calendar, survey.
In order to ease the PR introducing websockets in Odoo, introduce
the multi service. Indeed, the cross tab bus won't be necessary
anymore but there will still be a need to elect a main tab: some actions
should only be triggered once. To achieve this, the code electing the main
tab has been split with the one handling the longpolling. The crosstab
bus now relies on the multi tab service to known whether or not the
current tab is the main tab.
task-2053917
closesodoo/odoo#96174
Related: odoo/enterprise#29573
Signed-off-by: Sébastien Theys (seb) <seb@odoo.com>