Links one contract to another by creating the specified relationship. Provide the source contractId and a ContractRelationshipRequest containing the RelatedContractId, RelationshipFromType and RelationshipToType (for example: IsAmendmentFor, IsAmendedBy, IsRenewalFor, IsRenewedBy, IsNDAFor). Specify standard as well as custom picklist values configured for RelationshipFromType and RelationshipToType fields in RelatedAgreement object in the schema manager. The API returns the created RelatedAgreement with linked contract IDs and relationship details.