Multiday download from ECMWF CDS API

[jlmaurer]

Motivation and Context

RAiDER access ECMWF ERA-5 data from the ECMWF CDS API. Due to recent changes in how the era5-reanalysis-complete data is stored (tape archive) data access for model levels is taking a very long for single api calls, on the order of hours. Combine that with two required calls per date and a multi-date request, and you're waiting for days.

Description

This PR addresses the issue by bundling the request for all the days together when requesting model levels. The complexity is that pressure level data is still stored on a harddrive, so access is faster, but the multi-day download API does not work the same way. So, this PR updates both the pressure level and model level requests to use the fastest possible data access method.

This PR builds on #795, that PR should be merged first.

How Has This Been Tested?

Unit tests pass locally, and more unit tests have been added to test the new functionality.

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist:

• I have added an explanation of what your changes do and why you'd like us to include them.
• I have written new tests for your core changes, as applicable.
• I have successfully ran tests with your changes locally.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.