Allow usage of GDAL's virtual file systems

[jhkennedy]

Instead of modifying http://... paths with /vsicurl/, this instead:

• directly passes provided paths through to GDAL, allowing use of any GDAL virtual file system driver. Users would provide paths like:
  • local: /path/to/file/...
  • remote via url: /vsicurl/https://...
  • remote on S3 (allows access to requester pays buckets): /vsis3/...
  • etc.
• This however does mean that one cannot assume files are co-registered, so co-registration is always performed.

Also moves main driver inside a main() function, and does:

if __name__ == '__main__':
   main()

So that the test scripts can turned into entrypoints if vendored downstream (ideally, geo_autoRIFT would just provides these inside the package and add entrypoints for script access when the package is installed, but that can be tackled in a subsequent PR).

[jhkennedy]

Currently marked as draft to get other eyes on it while I'm testing -- will mark as ready for review when I've used this to run S1, S2, and L8 jobs.

[jhkennedy]

Marking this as ready for review because it will build fine in both the autoRIFT and ISCE2 conda-forge feedstocks.

Still have not utilized this end-to-end for S1, S2, or L8; working on that now.

[leiyangleon]

Just read through the changes, which looks great. Well done, @jhkennedy ! Happy to merge it.