Implement ERS sensor processing

[truth-quark]

Task: convert ERS processing in BASH to Python: https://github.com/GeoscienceAustralia/gamma_insar/blob/develop/process_ERS_SLC.bash

This port needs rework the BASH to fit Mitchell's 2021 framework for adding sensors and tests to the workflow.

Some ERS data is available here:

• gadi:/g/data/dg9/INSAR_ANALYSIS/ERS
• In MDSS insar/ERS_PROCESSING_BACKUP
  • to access, login to gadi, set PROJECT to dg9 and mdss ls -l insar/ERS_PROCESSING_BACKUP

[truth-quark]

Note ERS was last used by the InSAR team 7-8 years ago (~2015), before they switched to Sentinel data.