fix: type safe MicroAppEventOnEvent

[emanuel-braz]

Summary (Feature / Bugfix description)

• solves typedef MicroAppEventOnEvent payload with Type #61

This PR fixes/implements (types of changes)

• New feature (non-breaking change which adds functionality)
• Bug fix (non-breaking change which fixes an issue)
• Breaking change (fix or feature that would cause existing functionality to change)
• Chore, changes that do not affect the software behavior (docs, build process, configs, structures)

Requirements (if applicable)

• Have you lint your code locally prior to submission?
• All new and existing tests passed?
• Did you update the changelog file?
• Did you update pubspec.yaml?
• Have you written new tests for your core changes, as applicable?

Issues (if applicable)