chore: add workflow to mirror external repo

[betinacosta]

Description

add workflow to mirror external repo. This will not execute on github.com, but it needs to be here as well so its mirrored to internal repo. There is a check to avoid this from running on github.com

Related Issue

https://jira.tools.sap/browse/AFSDK-2934

Type of Change

Please check the relevant option:

• 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
• Code refactoring
• Dependency update

How to Test

N/A

Checklist

Before submitting your PR, please review and check the following:

• I have read the Contributing Guidelines
• I have verified that my changes solve the issue
• I have added/updated automated tests to cover my changes
• All tests pass locally
• I have verified that my code follows the Code Guidelines
• I have updated documentation (if applicable)
• I have added type hints for all public APIs
• My code does not contain sensitive information (credentials, tokens, etc.)
• I have followed Conventional Commits for commit messages

Breaking Changes

If this PR introduces breaking changes, please describe:

• What breaks
• Migration path for users
• Alternative approaches considered

Additional Notes

Add any additional context, screenshots, or information that would help reviewers.