ability to modify frontend bind

[vistrcm]

Hello, it will be great to allow users to modify the frontend.bind parameter to bind on UNIX sockets and ports other than 2375.

Use case: provide untrusted application access to the docker socket. The untrusted app can work only via a UNIX socket.

Proposed solution: #68

[basbebe]

Other use-case: Deploy inside a Podman pod and only bind to localhost.

[mtdcr]

Third use case: Run with --network none and make the frontend's Unix socket accessible in a shared volume.