Chart updates and release notes

[jaydeokar]

What type of PR is this?
release

Which issue does this PR fix?: N/A

What does this PR do / Why do we need it?: Release

Testing done on this change: N/A

Will this PR introduce any new dependencies?: N/A

Will this break upgrades or downgrades? Has updating a running cluster been tested?:
N/A

Does this change require updates to the CNI daemonset config files to work?: N/A

Does this PR introduce any user-facing change?: N/A

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

[Copilot]

Pull Request Overview

This PR updates AWS VPC CNI components from version v1.20.2 to v1.20.3 as part of a release process. The changes include version bumps across configuration files, Helm charts, and test scripts, along with release notes documentation.

• Update all container image tags and version references from v1.20.2 to v1.20.3
• Add changelog entries documenting the changes included in v1.20.3 release
• Improve shell script robustness with better quoting and loop structure

Reviewed Changes

Copilot reviewed 16 out of 16 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
scripts/run-cni-release-tests.sh	Updates CNI metrics helper version references in test configuration
scripts/generate-cni-yaml.sh	Updates VPC CNI version and improves script with better quoting and loop structure
config/master/*.yaml	Updates version labels and container image tags across all regional deployment configurations
charts/*/Chart.yaml	Updates Helm chart versions and app versions to v1.20.3
charts/*/values.yaml	Updates default image tags and version references in chart values
charts/*/README.md	Updates documentation to reflect new version numbers
CHANGELOG.md	Adds release notes for v1.20.3 with list of included changes

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