[IMP] web_editor, website: add individual Padding option for grid items
Before this commit, the "Padding" grid mode option, added in commit [1],
was impacting all the grid items at the same time, which was not
convenient since all these elements would have the same padding and
could not be styled individually.
This commit improves this option in order to modify the padding of the
grid items individually. The highlight effect, added in commit [2], when
changing the padding is still added.
[1]: https://github.com/odoo/odoo/commit/cc406afcea7bf5846233a9f97a4a8ac5f618f3ec
[2]: https://github.com/odoo/odoo/commit/f3f2c4c73ce08d3898b8c88e1ef045f7bbd1f624
task-3369695
Part-of: odoo/odoo#136683
Soukéina Bojabza
11418cc6f0