Allow `model2netcdf.ED2()` to process partial output from failed runs

[Aariq]

Description

Adds an argument process_partial (default FALSE) to model2netcdf.ED2() that allows it to work even on partial runs that have been interrupted and not produced as many .h5 files as expected based on the dates in settings.

Motivation and Context

Although ensembles of different lengths might screw up downstream analysis, sometimes you want to extract data from failed runs to inspect it.

Review Time Estimate

• [ ] Immediately
• [ ] Within one week
• [ ] When possible

Types of changes

• [ ] Bug fix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• [ ] My change requires a change to the documentation.
• [x] My name is in the list of CITATION.cff
• [x] I have updated the CHANGELOG.md.
• [x] I have updated the documentation accordingly.
• [x] I have read the CONTRIBUTING document.
• [ ] I have added tests to cover my changes.
• [ ] All new and existing tests passed.