Add DISABLE_CONTAINER_V6 to disable IPv6 networking in container network namespaces

[jdn5126]

What type of PR is this?
feature

Which issue does this PR fix:
#2483

What does this PR do / Why do we need it:
This PR introduces a new environment variable: DISABLE_CONTAINER_V6. When this environment variable is set, the tuning plugin will be chained in the AWS conflist (/etc/cni/net.d/10-aws.conflist) and configured to disable IPv6 networking in newly created container network namespaces. This is done to provide a solution to #2483.

If an issue # is not available please add repro steps and logs from IPAMD/CNI showing the issue:

1. Create an IPv4 cluster with containerd as the container-runtime (EKS 1.24+)
2. Create a pod
3. See that IPv6 is enabled on the loopback interface within the container network namespace regardless of host sysctls.

Testing done on this change:
Manually verified that conflist is rendered correctly and IPv6 is disabled in newly created container network namespaces. Verified that all integration tests pass following this change.

Automation added to e2e:
N/A

Will this PR introduce any new dependencies?:
No

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

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

Does this PR introduce any user-facing change?:
Yes

Introduce DISABLE_CONTAINER_V6 to disable IPv6 networking in container namespaces.

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

[jayanthvn]

Shouldn't this be default true for v6 clusters?

[jdn5126]

I don't think so, as we don't want to change default behavior. There could be some customers that rely on IPv6 being enabled

[jayanthvn]

nvm..it is not needed..we don't want the plugin..

[jayanthvn]

But lets add a line, we shouldn't set this for v6 clusters..

[jayanthvn]

lgtm..