Fix the isisStartup scripts for users outside of USGS systems

[cordellmichaud]

Description

• Fixes the issue isisStartup scripts fail outside of USGS systems #5478 raised by @rvwagner.
• The existence check for the data directory now correctly checks the new data directory path, rather than the old data directory path.
  • The ISISDATA variable assignment was corrected in Move application-related data into the repository. #3804 to use the new data path, but the existence check was mistakenly left uncorrected.
• The isisStartup scripts now function as they used to pre-4.4.0 and as they were intended to after the incomplete fix in Move application-related data into the repository. #3804.
• I understand these scripts are not used internally by most of those in the USGS and their continued existence in future versions of ISIS is uncertain. That said, this fix is minor and allows the scripts to function properly for those who do use them. Since they are still included in ISIS, they should at least be working as intended until their fate is decided through fuller discussion in the future.
• Added changelog entry for the fix.

Related Issue

#5478

How Has This Been Validated?

• Validated internally by the LROC team.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Documentation change (update to the documentation; no code change)
• Breaking change (fix or feature that would cause existing functionality to change)
• Infrastructure change (changes to things like CI or the build system that do not impact users)

Checklist:

• I have read and agree to abide by the Code of Conduct
• I have read the CONTRIBUTING document.
• My change requires a change to the documentation and I have updated the documentation accordingly.
• I have added tests to cover my changes.
• I have added myself to the .zenodo.json document.
• I have added my user impacting change to the CHANGELOG.md document.

Licensing

This project is mostly composed of free and unencumbered software released into the public domain, and we are unlikely to accept contributions that are not also released into the public domain. Somewhere near the top of each file should have these words:

This work is free and unencumbered software released into the public domain. In jurisdictions that recognize copyright laws, the author or authors of this software dedicate any and all copyright interest in the software to the public domain.

• I dedicate any and all copyright interest in this software to the public domain. I make this dedication for the benefit of the public at large and to the detriment of my heirs and successors. I intend this dedication to be an overt act of relinquishment in perpetuity of all present and future rights to this software under copyright law.

[github-actions]

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[github-actions]

The build and test suite have started for your pull request.

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[acpaquette]

Looks great! Thank you for handling this