Expand both DataBroker and TransactionChain with the following method:

    default FluentFuture<? extends CommitInfo> compact(LogicalDatastoreType datastore, InstanceIdentifier path) {
        return newWriteOnlyTransaction().commit();

with the appropriate documentation.

Implement these methods in mdsal-binding-dom-adapter minding the presence of DOMDataBroker.CompactExtension – if it is not present, the invocations should just succeed.