Refactor rhel8 + rhel8-variant scripts to use dnf

[tenthirtyam]

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Summary of Pull Request

Refactor scripts to use dnf for RHEL8 and RHEL8-variants.

Type of Pull Request

• This is a bug fix.
• This is an enhancement or feature.
• This is a code style / formatting update.
• This is a documentation update.
• This is a refactoring update.
• This is something else.
  Please describe:

Context of the Pull Request*

Refactor to use the DNF (Dandified YUM) software package manager. DNF is the successor of YUM (Yellowdog Updater Modified) and is the default package manager for RHEL8 and variants.

Related to Existing Issues

Issue Number: N/A

Test and Documentation Coverage

• Tests have been completed (for bug fixes / features).
• Documentation has been added / updated (for bug fixes / features).

Breaking Changes?

• Yes, there are breaking changes.
• No, there are no breaking changes.

[tenthirtyam]

✅ Reviewed
✅ Tested
🚢 Ship it.

[github-actions]

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