FMEPRD-151 Add April 16 Release Note

[alai97]

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Description

• Please describe your changes: Adds a release note from April that documents the ability to centralize control for flag update behavior in the React SDK.
• Jira/GitHub Issue numbers (if any): https://harness.atlassian.net/browse/FMEPRD-151
• Preview links/images (Internal contributors only): __________________

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• [ ] Successful preview build.
• [ ] Code owner review.
• [ ] No merge conflicts.
• [ ] Release notes/new features docs: Feature/version released to at least one prod environment.