Updated lronaccal to use time-dependent darkfiles for dark calibration (#4520)

* updated to use time dependent darks including darks for exp zero and also allowed passthru of certain special pixel types instead of nulling them

* Updated lronaccal.xml documentation

Updated documentation to provide more clarity regarding dark file correction/calibration options available to user.

* Updated formatting of text

* Added better documentation

* fixed formatting

* removed extra tabs

* Add radiance units label in lrowaccal output cube

* refactored code to allow callable for compatibility with gtest

* added gtests for 3 file types and made app callable

* Added changes for lronaccal to CHANGELOG.md

Added changes made to lronaccal and gtests to CHANGELOG.md.

Co-authored-by: Cordell Michaud <10409047+michaudcordell@users.noreply.github.com>