Drive stepper steps from workflow config

[NoopDog]

Need

The stepper currently renders all three steps it knows about for every workflow. These are

1. Reference Assembly
2. GTF Files
3. Paired-End Sequencing Data

This shows 3 in places where it is not required/desired.

Instead, we need to look at the workflow.yml parameters section, and only display workflow steps that are configured for the stepper (e.g. have a variable with a value we care about)

[d-callan]

see #580

[mvdbeek]

So the basics of this are implemented in #662 but I would rephrase this to say that we should build up both the stepper config and the values we send out in the landing request based on the workflow parameters, and track them based on the workflow input parameter name. There may for instance be optional inputs, or multiple inputs with separate fastqs (e.g. where samples need to be provided for treatment and control)