HLA-998: Proper handling of files which have SCI extensions completely zero in RAW

[s-goldman]

Resolves HLA-998

Closes #

This PR addresses the need to skip processing for exposures with science arrays of only zeros in ALL science extensions. One or multiple science extensions with all zeros will result in warnings for each extension.

This PR does not use no_proc_keys or no_proc_values, but does set do_process=False.

I also amended (and now use) the util.count_sci_ext function to return the indices of the science extensions if the return_ind flag is used.

I've also changed the variable related to the error of little-to-no exposure time (is_zero --> exposure_time_near_zero) in order to avoid confusion with our new error case.

Checklist for maintainers

• added entry in CHANGELOG.rst within the relevant release section
• updated or added relevant tests
• updated relevant documentation
• added relevant label(s)
• ran regression tests, post a link to the Jenkins job below.
  How to run regression tests on a PR

jenkins test

[mdlpstsci]

Some changes need to be made to accommodate multiple chips.

[mdlpstsci]

The utils.py module in drizzlepac has a function, count_sci_extensions.

Changes addressed.

[mdlpstsci]

All issues have been addressed.