An ansible role to set up an ssh tunnel and port forwardings from the remote machine to local machines

# Caution
Since the current debian version of sshd does not yet support dynamic configuration files (as in `/etc/ssh/sshd_config.d/*`), this role will **overwrite** your current sshd configuration! Normal ssh access on port 22 is still possible, but custom modifications will be lost on the remote machine.

# Variables you need to set
... e.g. in `group_vars`
- `ssh_tunnel_pubkey`: The complete line to be used in `authorized_keys`, e.g. "ssh-ed25519 AAAA[...]aU root@mylocalmachine"
- `ssh_tunnel_privkey`: The content of the corresponding private key file, including the BEGIN and END tags. It is highly recommended to put this inside an encrypted ansible vault.
- `tunneled_ports`: A list of port forwardings. Example:
  ```
  tunneled_ports:
  - exposed_port: 80 # public port at the remote machine
    ephemeral_port: 10080 # internal port at remote machine's localhost address. The ssh tunnel will fetch traffic from there
    dest_host: my-internal-http-server.local.domain.tld # domain or IP address of the destination machine. Must be reachable form the local machine.
    dest_port: 80 # open port at the destination machine
    protocols: ["tcp"] # list of protocols for this forwarding. "tcp" and "udp" are supported.
  ```