Explore ansible-runner as an execution backend

Investigate whether [ansible-runner](https://ansible.readthedocs.io/projects/runner/en/latest/) is a good fit for the Kestra Ansible plugin as an alternative (or complement) to invoking `ansible-playbook` directly.

ansible-runner is the execution engine used by AWX/Ansible Automation Platform. It is designed to run Ansible from a controller against remote hosts and provides a structured "private data directory" layout (`env/`, `inventory/`, `project/`, etc.) for injecting variables, secrets, inventory, and project files into a run. This structure could map to Kestra's existing secrets management.

To validate:
- whether ansible-runner provides meaningful advantages over the current direct `ansible-playbook` invocation (e.g., richer event stream, artifacts, status, stdout/stderr separation, fact caching).
- Evaluate how Kestra secrets and variables could be injected via the `env/` directory (`envvars`, `extravars`, `passwords`, `ssh_key`).
- Assess support for distributed/remote execution scenarios where the runner is executed on a different host than Kestra.

The issue names no repository files or tests; start by locating the current direct ansible-playbook invocation and review the ansible-runner documentation linked in the issue. Compare execution events, artifacts, variable and secret injection, and remote execution support, then document whether ansible-runner offers a practical advantage and how it could fit Kestra.

Written by the indexing model from the issue text.