(as part of #2880)

• modified a few of the steps in the release process workflow
• modified the release notes to reflect the contents in the 6.4.0 release
• modified the Maven pom.xml to include the step to upload the artifacts to Sonatype Nexus and also sign the keys in a specific way

Make sure that:

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• You have created a feature request first to discuss your contribution intent. Please reference the feature request ticket number in the pull request.
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• You submit test cases (unit or integration tests) that back your changes.