Move pipeline scheduling to step functions

[ARMmaster17]

Is your feature request related to a problem? Please describe.
The code for pipelines is getting a little messy. There are multiple implementations of scheduling code across all three operating modes.

Describe the solution you'd like
I think that it would be a good idea to move scheduling-related stuff to dedicated steps that emit a context when the timing is right. This would allow us to migrate SA/HA/DP mode pipelines to all essentially act like DP mode, making the implementation much simlpler.

Describe alternatives you've considered
N/A

Additional context
N/A

Implementation

• Pipeline should stop if len(context) == 0 #78
• Create arbitrary locks with DataContext in pipeline steps #80