Add PR template + CONTRIBUTING.md and update gitignore

[buidav]

🗣 Description

• Add back ignoring various out report files to the .gitignore but add an exception to the sample-report.
• Add a CONTRIBUTING.MD and an updated PR template.
• Tiny fix for a broken link in the README.
• Update pylint to lint in the same scenarios and the rego linter.

💭 Motivation and context

To add and fix various issues found in misc files

🧪 Testing

Clicked on the various links throughout the updated files to see if they worked.

✅ Pre-approval checklist

• This PR has an informative and human-readable title.
• Changes are limited to a single goal - eschew scope creep!
• If applicable, All future TODOs are captured in issues, which are referenced in the PR description.
• The relevant issues PR resolves are linked preferably via closing keywords.
• All relevant type-of-change labels have been added.
• I have read and agree to the CONTRIBUTING.md document.
• These code changes follow cisagov code standards.
• All relevant repo and/or project documentation has been updated to reflect the changes in this PR.
• Tests have been added and/or modified to cover the changes in this PR.
• All new and existing tests pass.

✅ Pre-merge Checklist

• This PR has been smoke tested to ensure main is in a functional state when this PR is merged.
• Squash all commits into one PR level commit using the Squash and merge button.

✅ Post-merge Checklist

• Delete the branch to clean up.
• Close issues resolved by this PR if the closing keywords did not activate.

[adhilto]

Looks great