[IMP] website: vertically center the images in gallery slideshow
[IMP] website: vertically center the images in gallery slideshow

Note: the design of the whole snippet should be improved

Part of https://github.com/odoo/odoo/pull/36803
task-2070930

closes odoo/odoo#36803

Signed-off-by: Quentin Smetz (qsm) <75b324bb495ac8d4f83496f7c52eda774af7ed7a@odoo.com>

ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo