Git Output Artifacts

# Summary

Currently Git Artifact only supports input, providing support for output would be great. I can see this providing credentials is already supported via secrets, theoretically the minimum extra field required would be a commit message

# Use Cases

Easy workflows that needs to update remote git repositories, such as argocd configuration repos.

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**Message from the maintainers**:

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The issue names Git Artifact input support but no files, tests, or entry points. Start by locating the existing Git Artifact implementation and its input handling, then determine how output artifacts, credentials, repository updates, and commit messages should be specified. Done means a workflow can update a remote Git repository through the artifact and the behavior is covered by tests.

Written by the indexing model from the issue text.