aws-vpc-cni and cni-metrics-helper chart updates for 1.15.1 release

[jdn5126]

Issue

N/A

Description of changes

This PR contains chart updates for aws-vpc-cni and cni-metrics-helper for v1.15.1 release. The changes are:
aws-vpc-cni:

• image tag update for VPC CNI and network policy agent containers
• --enable-policy-event-logs arg for network policy agent container, paired with configurable nodeAgent.enablePolicyEventLogs in values.yaml (default false)
• data -> binaryData fix in ConfigMap
• VPC_CNI_VERSION environment variable
• ENABLE_V4_EGRESS environment variable

cni-metrics-helper:

• image tag update

Checklist

• Added/modified documentation as required (such as the README.md for modified charts)
• Incremented the chart version in Chart.yaml for the modified chart(s)
• Manually tested. Describe what testing was done in the testing section below
• Make sure the title of the PR is a good description that can go into the release notes

Testing

Manually verified that chart can be applied to cluster.

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

[jaydeokar]

lgtm