[AG-838] Support independent transforms

[BWMac]

This PR refactors the transform module by splitting up transform.py. From transform.py, the apply_custom_transformations function is moved to process.py since it is only used there, and it only applies the transformations already defined in transform. The functions standardize_column_names, standardize_values, rename_columns, and nest_fields are all moved to etl/utils.py to consolidate utility functions for all etl modules, and because they are all used in more than one other module. etl/transform becomes a submodule only containing custom transformation scripts to make contributing new transformations and importing them where needed (in process.py) simpler.

process.py is updated to account for all of these changes.

A tests/transform directory was created and the existing transform tests were split into test_utils.py and transform/test_genes_biodomains.py.

[thomasyu888]

Have an initial few comments. Thanks Brad!

[thomasyu888]

🔥 LGTM! Going to pre-approve. Will wait for @JessterB and @jaclynbeck-sage to comment. There are many things that can be improved so that it becomes easier to contribute.

We can iterate on adding a CONTRIBUTING.md section after this gets merged in.

[JessterB]

I ran my current data validation process for the new version of the files generated by this PR to make sure nothing went sideways during the refactor, and everything is looking good!

[jaclynbeck-sage]

Everything looks good! What a colossal amount of work, thank you Brad!!