Add support for multiple environments

[AaronFeledy]

In the event that there are multiple remote environments, such as a dev and live environment, Lando Scripts should be able to switch between interacting with either without making changes to the config file.

Users should be able to define the environments separately within their config file, then optionally specify the environment to use when executing a command that interacts with a remote environment.

E.g. lando script pull-db --env=live might pull the db from the live environment.