Could projection task run in two steps (first on some wells, then on some others)

[tcompa]

The intended use case would be:

1. Run projection task (and possibly the other tasks of the workflow) for a given well
2. Re-run it for a different well

[jluethi]

I think what we'll need to do is adapt the init for it: It's not always supposed to overwrite an existing OME-Zarr HCS plate, but to extend it if it already exists. As long as the actual images in the target wells don't exist yet, that shouldn't be an "overwrite" operation