[SDPA-6115] - Add aria-atomic attribute to rpl-form-alert component

[ChrisCampbellCodes]

Motivation and Context

JIRA issue: https://digital-engagement.atlassian.net/browse/SDPA-6115

Changed

1. Added aria-atomic="true" attribute to rpl-form-alert component

Screenshots

How Has This Been Tested?

Types of changes

• [ ] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [ ] Improvement/refactoring (non-breaking change that doesn't add any features but makes things better)

Checklist

• [ ] I've added relevant changes to the documentation.
• [ ] I have added tests to cover my changes (if not applicable, please state why)
• [ ] My change requires a template update for create-ripple-app.
• [ ] I have added template update script for next release.