Parallelize presync steps as advisable

[jbornemann]

We should be able to use batch:split/batch:flow to parallelize presync steps such as deleteBeforeWrite, and namespaceSync. Parallelizing clientWorkflowOff may not be safe, as the client could have workflows around deletion of nodes; and we may run into a situation where nodes are deleted, and workflows are started, before the workflows are turned off.

[jbornemann]

@sagarsane

[jbornemann]

Presently, this seems to be too much of micro-optimization to be prioritized. The landscape presents many big performance wins still to be accomplished