Save install-subnet-chain commands in a file

[exdx]

When using avalancheup-aws apply the end result is a list of endpoints and commands that can be run, for things like installing a new chain on the network. These commands are very helpful, but since they are only emitted to stdout, they can get lost in the terminal. I think writing the output of apply to stdout and a file (with the same aops- convention as the spec yaml file) could be helpful as a resource for users to retain access to all the auto-generated commands across terminals.

[exdx]

Could be an optional flag versus a default behavior