Migrate the collimated (offspec) reduction workflow

[nvaytet]

The collimated data reduction for OFFSPEC in the old ess repo should be migrated here.

The workflow is quite similar to the divergent reduction workflow.

[nvaytet]

@arm61 said he would do this, also to learn how to use sciline.

[SimonHeybrock]

@arm61 Are you still planning to work on this, or should we take action ourselves?

[arm61]

Feel free to complete it if you have a chance. My time has been too limited.