Legal basis: consider modeling the specific rules that apply to the legal basis

[yolile]

In the UK, some procurement processes under the same legislation have different rules depending on the buyer, items, etc. For example, if they are part of a "special regime" or "above threshold".

Currently, there is no standard way of disclosing these rules.

One option to model this is to change the legalBasis object to something else instead of a Classification object (since the special regime and thresholds are specific to the legal basis)

Also, instead of adding fields directly to the tender object (e.g., tender.crossBorderLaw) we could group them in a new tender.legal object that has tender.legal.basis and something else.

Originally discussed as part of CRM-8513