Add "sync" option to DICOMweb push/pull tasks which will query the local/remote server to see if a study already exists before queing for transfer

Due to multiple factors (timeout values, network instability, ... ), it's relatively common for DICOMweb transfers to fail. For that reason, tools are needed to efficiently re-queue items.

An option needs to be added to the CLI tool to allow for "sync" of a remote and local server. When passed, the sync flag will issue a query to the server where the data is to be copied to see if the resource is already present. If so, the transfer of that reference will be skipped.

For push of resources from a local machine to a remote peer, the query will need to be executed on the remote system. For pull, the query will need to be executed on the local system.