feat: support user-hooks for additional file changes

[apricote]

This is required in https://github.com/ansible-collections/hetzner.hcloud as it uses antsibull to manage a CHANGELOG.rst and this is kinda a requirement for the ansible-collections namespace.

Open Challenges:

• How should this handle dependencies that are missing in the env? In GitHub Actions this should not be a problem, but on gitlab-ci we are running in a single binary container that does not have access to any other runtimes/programs for the user.

[jooola]

For Gitlab, we might want to leverage the step runner (experimental), that behaves a bit more like Github Actions.

• https://docs.gitlab.com/ci/steps/
• https://handbook.gitlab.com/handbook/engineering/architecture/design-documents/gitlab_steps/
• https://gitlab.com/gitlab-org/step-runner