Add lock to execute of MDFWriter and enable multi-threaded MDF writing

The MR adds a lock to the execute of MDFWriter to prevent multiple threads writing at the same time. In addition remove the protection in the configuration to allow writing of MDFs when running multi-threaded.

This is useful when running Moore manually as it allows to process large amounts in one process on a single node.

Note this MR only affects offline running, so optimizing where to put the lock is not super critical. The online processes use a different service to write files.