Update isd_generate.py

[thareUSGS]

add in PROJ like options for radius names ("-a", "-r", "--radius", "-b")

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[thareUSGS]

I assumed this would automatically get added on top of this pull request. I guess I did it in the wrong order (or permissions are different)? https://github.com/DOI-USGS/ale/pull/486

In more testing of GXP, we still need a sphere override for users.