Update notebooks for eta file creations

[mlee03]

Description In this PR, generate_eta_files.ipynb has been added. This notebook will generate the eta79.nc and eta91.nc files that are used in tests/main. This notebook will be used as part of CI to generate input files on-the-fly.

In addition, the notebooks generate_eta_file_netcdf.ipynb and generate_eta_file_xarray.ipynb have been removed. Contents of generate_eta_file_xarray.ipynb are contained in the new notebook. And since the files can be generated with generate_eta_files.ipynb, generate_eta_file_netcdf.ipynb has been removed.

Fixes # (issue)

How Has This Been Tested? The jupyter notebook was converted to a python script (for convenience) and executed. The contents of the generated netcdf files were checked against the original data in class HybridPressureCoefficients

Checklist:

• [x] My code follows the style guidelines of this project
• [x] I have performed a self-review of my own code
• [x] I have commented my code, particularly in hard-to-understand areas
• [x] I have made corresponding changes to the documentation
• [x] My changes generate no new warnings
• [x] Any dependent changes have been merged and published in downstream modules
• [x] New check tests, if applicable, are included

[mlee03]

I was just thinking that especially when the goal is just to write out files, perhaps it'd be better to change move/convert the notebook to a python script in this PR. @fmalatino, this PR is not readly

[fmalatino]

I see the PR is re-opened and all tests pass, @mlee03 is this ready to be merged?

[mlee03]

'tis ready