`rofl create`: Name first deployment after a network instead of `default`

[matevz]

• When running rofl create, name the deployment by the selected network name (e.g. testnet, mainnet).
• Add a deployments.<deployment_name>.default bool field. Use this default deployment for rofl commands then, if no --deployment flag provided.
• Add oasis rofl set-default <deployment> command which sets the default deployment.
• Add a Hint for set-default command to error message asking you to select a deployment.

Context: A few ROFL projects have been built and .orc sent to me for deployment. It's annoying when there is a bunch of .orc files in your folder and don't know which node you need to copy them over to (mainnet or testnet).

Alternatives

• There could be a default_deployment global bool field instead of deployments.<deployment_name>.default
• We could also assume the first deployment in rofl.yaml as default one (Makefile like). But since maps in go are not deterministic, this may be very tricky to implement.