Update stacks-node and add stacks-signer

[hugocaillard]

• update stacks-node image
• update stack-stx (new arguments in pox-4 for stack-stx and extend)
• add the signer image to the devnet

[sabbyanandan]

@hugocaillard: It is probably too early right now, but when the time is right, it'd be good to get a sense of the Docker daemon's compute requirements (i.e., what is a reasonable CPU, disk, and memory defaults?), including the additional resources (for instance, a new "signer image") that need to be spun up. We can add/update the pre-requisite section in docs/README.

In the Platform, we will automatically apply and handle the dynamic allocation of new resource requirements for each user.