OPERA R4 PGE Engineering Release 2.0

Engineering Release v2.0 for the OPERA R4 PGE. This release comprises the Dynamic Surface Water Extent (DSWx) from NISAR (NI) PGE, which still wraps the initial "Interface" delivery of the corresponding SAS. This update adds support for output product validation and generation of an initial (dummy) ISO XML product.

What's Changed

• DSWx-NI Output Product Validation #437 by @JimHofman in #444
• 438 dswx ni integration test framework addition by @rjbdev05 in #448
• 439 dswx ni filename validation by @JimHofman in #451
• add the validation checks in .ci.scripts by @rjbdev05 in #452
• flake8 cleanup by @JimHofman in #453
• DSWx-NI ISO XML Generation by @collinss-jpl in #454
• Release 4.0.0 ER-2.0 by @collinss-jpl in #457

Full Changelog: 4.0.0-er.1.0...4.0.0-er.2.0