[FIX] web: support readonly attribute on toggle_button widget

before this commit: applying readonly attribute on toggle_button doesn't work,
toggle_button still clickable and value is still changed even though widget is
readonly, there is no effect of readonly attribute on toggle_button widget.

after this commit: if toggle_button widget has readonly attribute then it will
not be clickable, button of toggle_button will be disabled so that user can
easily understand that element is not clickable.

task-2339995

closes odoo/odoo#76426

Signed-off-by: Aaron Bohy (aab) <aab@odoo.com>