fix: restore onchange on tender line form

[lepistone]

This gives to the product field the same onchange we have in the tree view.

One side effect of this is that by default this sets the quantity to 1 (instead of zero). Lines with quantity zero are easily overseen and give problems later when bids cannot be selected because of differing quantities.

[coveralls]

Coverage remained the same when pulling 06a383e01c7e346021d6fe4cde60c704064ff63e on lepistone:fix-tender-onchange-product into b94523f0bef590e1fa806088dfd025e65182d684 on OCA:8.0.

[rdeheele]

:+1:

[foutoucour]

:+1:

[guewen]

:+1: