remove workarounds from custom pod controller and refactor code

[abhipth]

Description of changes:

• Removing workaround from the memory optimized Pod controller to pass Delete Event with request.
• Renaming file and structs, interfaces names to more descriptive names.
• Refactor code so it's easier to add new resource like IPv4 Address on top of Pod ENI.

Testing for the Change

• Ran Integration test in loop (x5 times) - Passed
• Ensure memory doesn't increase as the Number of Pods increases - Passed
• Ensure existing Pod's networking is not removed once the controller restarts - Passed

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[orsenthil]

I am not an authority on this code base. I looked it, trying to understand the change and adding comments.

Please take other reviewer's comments over mine.

[orsenthil]

• This https://github.com/aws/amazon-vpc-resource-controller-k8s/pull/44/files#r690825698 seems to be only significant comment that could change the code a little again.

• Rest of the comments are to improve readability and comprehensibility.

• There are unused local variables through out the code, perhaps linter will help remove them all.

[orsenthil]

@abhipth - I am done reviewing. Please address these comments and I could review again and approve it.

[orsenthil]

The unit tests failure is due to this upstream issue - kubernetes-sigs/kubebuilder#2311

[orsenthil]

LGTM. thank you.