Adding change log and release notes for v1.20.4

[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?: N/A

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 version references throughout the codebase from v1.20.3 to v1.20.4 to prepare for the v1.20.4 release of the AWS VPC CNI. The changes include updating version numbers in configuration files, scripts, Helm charts, and adding release notes to the changelog.

• Updates all version references from v1.20.3 to v1.20.4 across configuration files and scripts
• Adds changelog entries documenting the changes included in v1.20.4
• Updates Helm chart versions and documentation to reflect the new release

Reviewed Changes

Copilot reviewed 16 out of 16 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
scripts/run-cni-release-tests.sh	Updates CNI metrics helper image tags and default version references
scripts/generate-cni-yaml.sh	Updates VPC_CNI_VERSION variable to v1.20.4
config/master/*.yaml	Updates version labels and container image tags across all regional configurations
charts/*/Chart.yaml	Updates Helm chart versions and appVersions
charts/*/values.yaml	Updates default image tags and VPC_CNI_VERSION values
charts/*/README.md	Updates version references in documentation tables
CHANGELOG.md	Adds v1.20.4 release notes with list of included changes

---

_{Tip: Customize your code reviews with copilot-instructions.md. Create the file or learn how to get started.}