Fix call to ELP

[nden]

This PR does two things

• Fixes the way the exposure level pipeline and a step are called by using the .call method.
  There are two ways to execute a step or a pipeline.
  .call : combines parameter values from the defaults in the code, CRDS parameter files and user supplied parameters
  .run: uses the default parameter values in the code and ignores parameter files in CRDS.
• Changes the step name : source_detection to source_catalog as this has changed in the pipeline. The change was made in romancal v 16.

@tddesjardins