iptables: refactor helper, add RuleSet

[nadiamoe]

Description

This PR continues the iptables refactoring work initiated by #357, by keeping a simple helper that works with structured rules and putting the auto-removing logic into a new object called RuleSet.

The TrafficRedirector has been refactored to use the new helper, but not the RuleSet.

Checklist:

• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works.
• I have run linter locally (make lint) and all checks pass.
• I have run tests locally (make test) and all tests pass.
• I have run relevant integration test locally (make integration-xxx for affected packages)
• I have run relevant e2e test locally (make e2e-xxx for disruptors, or cluster related changes)
• Any dependent changes have been merged and published in downstream modules
  

[pablochacin]

What is the reason for changing the convention we have been using of not creating a different package for tests? Does this bring any advantage? I prefer to maintain consistency across packages

[nadiamoe]

I think I made this change out of habit as I was testing exported functions only, I agree we should keep consistency. I can change it real quick :)

[pablochacin]

LGTM. I only not fully in favor of changing the implicit convention of not using test packages. I wold prefer to maintain consistency across the project.