fix: fixing issues found in 2.19.0 testing

[bejjrajesh]

Proposed changes

This MR will contains changes identified after nim 2.19.0 release went yesterday. Below are the issue details.

1. When using -f fqdn option, the new certs are not generated unless existing certs are deleted. So added the change to delete existing certs and generate new certs using the -f option.
2. Redhat systems are downgrading the nim to 2.18.0 because of the logic issue. Fixed and verified it.

Checklist

Before merging a pull request, run through this checklist and mark each as complete.

• I have read the contributing guidelines
• I have signed the F5 Contributor License Agreement (CLA)
• I have ensured that documentation content adheres to the style guide
• If the change involves potentially sensitive changes, I have assessed the possible impact
• If applicable, I have added tests that prove my fix is effective or that my feature works
• If applicable, I have checked that any relevant tests pass after adding my changes
• I have updated any relevant documentation (README.md and CHANGELOG.md)
• I have rebased my branch onto main
• I will ensure my PR is targeting the main branch and pulling from my branch from my own fork

Potentially sensitive changes include anything involving code, personally identify information (PII), live URLs or significant amounts of new or revised documentation.

Please refer to our style guide for guidance about placeholder content.

[mjang]

Approving with some "typo-level" comments.