docs: add dual-stack iptables api model

[aramase]

Reason for Change:

• Adds iptables api model for dual-stack
• Updates dual-stack docs

Issue Fixed:

Credit Where Due:

Does this change contain code from or inspired by another project?

• No
• Yes

If "Yes," did you notify that project's maintainers and provide attribution?

• No
• Yes

Requirements:

• uses conventional commit messages
• includes documentation
• adds unit tests
• tested upgrade from previous version

Notes:
/cc @lachie83

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[jackfrancis]

Any changes we should make to the api model that we run tests against?

See test/e2e/test_cluster_configs/dualstack.json

[codecov]

Codecov Report

Merging #4185 (70162cd) into master (1cd06c6) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #4185   +/-   ##
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  Coverage   73.38%   73.38%           
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  Files         135      135           
  Lines       20804    20804           
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  Hits        15267    15267           
  Misses       4562     4562           
  Partials      975      975           

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[aramase]

@jackfrancis No changes in the test cluster config. I'm adding the same model with iptables to the examples/dualstack dir.