Custom junit properties

[zcsteele]

Summary

Add custom JUnit properties to the report file output (Official Maestro documentation & example at https://docs.maestro.dev/maestro-flows/workspace-management/test-reports-and-artifacts#custom-properties)

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update
• Refactoring (no functional changes)

Changes Made

• Add the 'properties' definition to relevant structs ('Config', 'FlowEntry' and 'FlowDetail')
• Add a new output generator to pkg/report/junit.go which adds additional properties elements for any custom properties provided in the flow file
• Additional test case TestBuildJUnitXMLCustomProperties to verify the XML generated when a flow specifies custom properties

Related Issues

Fixes #84

Testing

• Tests pass locally (make test)
• Linting passes (make lint)
• Added tests for new functionality
• Tested manually with sample flows

Checklist

• Code follows project style guidelines
• Self-reviewed the code
• Added/updated documentation as needed
• No breaking changes (or documented if breaking)
• CHANGELOG.md updated (for notable changes)