Added enviroment variable to allow ipamd to manage the ENIs on a non schedulable node

[rajeeshckr]

What type of PR is this?
feature

Which issue does this PR fix:
#2265

What does this PR do / Why do we need it:
TLDR, we need the ipamd to allocate pod IP from non primary ENI on a scheduling disabled node to run a key cluster daemonset component.
Details regarding the bug can be found under the issue

Testing done on this change:
Tested with unit test TestIncreaseIPPoolCustomENIOnNonSchedulableNode.

Automation added to e2e:
No

Will this PR introduce any new dependencies?:
No

Will this break upgrades or downgrades. Has updating a running cluster been tested?:
No

Does this change require updates to the CNI daemonset config files to work?:
No

Does this PR introduce any user-facing change?:
No

ipamd can manage ENIs on nonschedulable node when `AWS_VPC_K8S_CNI_MANAGE_ENIS_ON_NON_SCHEDULABLE_NODE` is set to `true`

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[jdn5126]

Change overall looks good to me, just a few nits. Can you also add the environment variable to the README.md? You can use version v1.13.0+.

And did you confirm that this fixes your issue? Like you build your own image, installed it, and this fixed things?

[jdn5126]

@rajeeshckr looks like some bad merge conflict resolution here. Can you fix the diff so that it only shows your changes?

[rajeeshckr]

@rajeeshckr looks like some bad merge conflict resolution here. Can you fix the diff so that it only shows your changes?

@jdn5126, I have tested this building and running with the new image. Looks good to me! Thanks for helping with the review!

[rajeeshckr]

I have updated the README.md, we are using v1.12.0. Is there a chance of cherry-picking this to that release?

[jdn5126]

Thanks for making these changes! Just two last nits and then we can kick off an integration run against this change

[jdn5126]

I have updated the README.md, we are using v1.12.0. Is there a chance of cherry-picking this to that release?

Thanks for cleaning this up and adding additional test coverage! And yep, this will end up in the next 1.12 release, so v1.12.6, which we are working on now

[jdn5126]

Integration test run status is here: https://github.com/aws/amazon-vpc-cni-k8s/actions/runs/4349737321

[jdn5126]

Integration test passed, so merging now. Thanks for the help, @rajeeshckr !