[FIX] website: avoid marking some non-editable tab panes as editable

This reviews [1] (in particular changing my mind about [2] upon further
review). Indeed this was marking potential non editable tab panes as
editable by searching the whole DOM instead of editable savable zones.

In the end, what is searched for is also reviewed. Instead of searching
for a very specific structure, we now mark all oe_structure which are
direct children of tab-pane as editable (if in an editable zone) and
their parent (the tab-pane who have a direct oe_structure child) as
readonly.

[1]: https://github.com/odoo/odoo/commit/5fd99855654d220bafb8887cd0ae267042836d4b
[2]: https://github.com/odoo/odoo/pull/109430#discussion_r1115792052



closes odoo/odoo#113605

Signed-off-by: Quentin Smetz (qsm) <qsm@odoo.com>