Add elastic IP annotation to front end NLB

[swarner1033]

Issue

#4300, #2782 (comment)

Description

• Adds a new annotation alb.ingress.kubernetes.io/frontend-nlb-eip-allocations.
• While I was working on this I noticed a way to fix another issue that I saw where even if you have an internet-facing NLB it will get assigned private subnets if the ALB is internal. This does not match what it stated on the subnet discovery page
• Abstract out subnet construction to make it more extensible.

How

1. Read annotations
2. Validate subnets and use existing ResolveViaDiscovery() to get based on tags if not present in annotations - new function
3. Validate EIPs - new function
4. Construct subnet mapping- existing function.

Checklist

• Added tests that cover your change (if possible)
• Added/modified documentation as required (such as the README.md, or the docs directory)
• Manually tested
• Made sure the title of the PR is a good description that can go into the release notes

BONUS POINTS checklist: complete for good vibes and maybe prizes?! 🤯

• Backfilled missing tests for code in same general area 🎉
• Refactored something and made the world a better place 🌟

[k8s-ci-robot]

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[k8s-ci-robot]

Hi @swarner1033. Thanks for your PR.

I'm waiting for a kubernetes-sigs member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

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[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: swarner1033 / name: Sophie Warner (c818065, c4d6986, de5599f, 1c3cd3c, cf7de7c, cdba2ec, ec6fbe8, eaad2ca, 218bcdf, 59a98e2, 8627f69, ddcf64d, 7ff033e, 8a5d3aa, 7ccad6c, a5fd2d6, 4a51be9, 6ecc2d9, 14c8c52, 8e92ce3, 618bc1d, 28ed8e5, 8f5eba9)
• ✅ login: 1ms-ms / name: ms (d902d3a)
• ✅ login: swarner1033 / name: swarner1033 (627e663)
• ✅ login: shraddhabang / name: Shraddha Bang (31c45b0)

[zac-nixon]

/ok-to-test
/lgtm

[zac-nixon]

Thanks for taking the time to do this! Looks good.

[shraddhabang]

/lgtm

[swarner1033]

Have rebased and now e2e tests pass. Could I have another LGTM pls @shraddhabang @zac-nixon?

[zac-nixon]

/lgtm
/approved