[13.0] l10n_be: migration account.account.tag

[remytms]

This migration script is a new approach in migrating account.account.tag for belgian localisation.

This PR superseeds #3675 .

Standard taxes are better covered, e.g. group taxes. It also tries to cover custom taxes.

[remytms]

@marielejeune this pr may interest you. :)

[marielejeune]

Thanks @remytms I ping @qgroulard who will continue working on our migration during my maternity leave. :)