NewUpSyncer returns a new controller which upsyncs, through the Upsyncer virtual workspace, downstream resources which are part of the upsyncable resource types (fixed limited list for now), and provide the following labels: - internal.workload.kcp.io/cluster: <sync target key> - state.workload.kcp.io/<sync target key>: Upsync and optionally, for cluster-wide resources, the `kcp.io/namespace-locator` annotation filled with the information necessary identify the upstream workspace to upsync to.

NewUpSyncerCleanupController returns a new controller which will cleanup any upsynced upstream resource if the corresponding downstream resources doesn't exist.

ResourceVersionAnnotation is an annotation set on a resource upsynced upstream that contains the resourceVersion of the corresponding downstream resource when it was last upsynced.