[bug/ci] Make auto-install.sh capable of running in non-interactive mode

Describe the bug
When running deploy/auto-install.sh in a CI environment (GitHub Actions) with input piped via heredoc or printf, the script hangs waiting for user input. This appears to be due to prompts reading from /dev/tty instead of standard input, which is not available in non-interactive environments. As a result, automation steps that previously worked now get stuck indefinitely.

Steps To Reproduce

See https://github.com/openwisp/docker-openwisp/pull/487.

1. Set up a GitHub Actions job on ubuntu-24.04 runner.
2. Run a step that pipes input to auto-install.sh, for example:

   printf "edge\n./.env\n" | sudo -E ./deploy/auto-install.sh
   

3. Observe that the script starts, prints the welcome message, but hangs at the first prompt for input.

Expected behavior
The script should:

Accept piped input from stdin in addition to /dev/tty.

Or allow passing all required inputs via command-line arguments or environment variables (e.g., --version, --env-file) so it can run fully non-interactively in CI environments.

System Information:

OS: Ubuntu 24.04 LTS (GitHub Actions ubuntu-24.04 runner)
Docker version: 27.0.3, build 7d4bcd8
Browser: N/A

Start with deploy/auto-install.sh and reproduce the hang in a GitHub Actions Ubuntu 24.04 step using the printf command from the issue. Trace how prompts read from /dev/tty versus stdin; done means the required inputs can be supplied non-interactively without hanging, while preserving the existing interactive behavior.