Add effective date selection when syncing quote items to existing Autotask contracts

When using the "Add quote items to contract" feature to sync services to an existing Autotask contract, there is currently no option to set an effective date. The service is added using the contract's original start date (e.g., Jul-01-2020), rather than a current or user-defined date.

For new contracts created in Salesbuildr, an effective date can be set before syncing. This same capability should be available for existing contracts.