Pool: Enforce Own Company Data Sharing Constraints

### Description

As a golden record process provider I don't want dataspace participants to share sites of other companies. If a dataspace participant shares a site of another company the golden record process should reject that site with an appropriate error message.

At the same time dataspace participants should be able to share sites of their own or managed companies.

Upon processing a golden record task with site information the Pool should check whether the site has been shared by its owner or the managing company of its owner.

### Acceptance Criteria

- [ ] The Pool rejects business partners with site information if the business partner is not shared by a dataspace participant or its managing legal entity
- [ ] When upserting business partner records in the Pool, own records shared by an owner should have the confidence criterion isSharedByOwner set to true

### Additional Information