Well, it might be kind of overkill, but basically you could use matrix to bridge to signal and then use a bot to do automatic answers.
The matrix ansible docker deploy playbook would be able to install everything you'd need for that:
- synapse, the matrix server
- mautrix-signal, the bridge to signal
- maubot, which you could configure to do auto replies
All of those components are open source.
Maybe one like this?