Generating jedivar yamls

[delippi]

For running DA cycled experiments, we need to implement a method to build the jedivar.yaml from the validated yamls in RDASApp. We will eventually want to do this with JCB, but not right now.

It seems the best approach is to generate a template at the time of configuring the workflow, then update that template for each cycle replacing date strings. We shouldn't have to rebuild the jedivar.yaml each cycle... although we could if we needed to for some reason.