docs(0074): add business partner relation extensions

[nicoprow]

Extends the Business Partner Relation section of CX-0074 with four concepts already present in the reference implementation but not yet covered by the standard:

• Two new relation types — IsOwnedBy (majority ownership > 50 % between legal entities) and IsReplacedBy (an additional address becomes the new legal address of a legal entity, triggering address type transitions in the output).
• Validity periods — a relation can carry one or more dated intervals (ValidFrom / ValidTo) to express when it is active, including interrupted histories.
• Reason code — a code selected from the Pool operator's catalogue documenting why the relation was established. Mandatory for IsReplacedBy, optional otherwise.
• Golden Record Relations in output — the output representation of a legal entity and an address now embeds the complete set of Pool-level relations involving that record, refreshed whenever the underlying Golden Record changes.

The class diagrams are updated accordingly.

Change Request

https://github.com/catenax-eV/product-standardization-prod/issues/667