Unified solution for configuring CA scripts args using JSON

!581 (merged) introduced a way to configure ca script args from the json config file, which is great for reproducibility.

The downside to the current approach is that

1. it's only implemented for the trigger
2. configuration is split between CLI and JSON rather than unified
3. it doesn't support configuring of the base dumper args

We should improve this by making the dumper.py args configurable from JSON.

One solution to this would be to use a tool like jsonargparse, which powers the CLI in salt. This might be overkill for this package though..

Relates to #131 (closed)