Lagoon shell

Is your feature request related to a problem? Please describe.
Having to type lagoon --project really-long-project-name --environment also-really-long-environment-name gets old.

Describe the solution you'd like
A REPL shell for Lagoon that stores some context (and shows it in the prompt). Context might include:

• $LAGOON_PROJECT
• $LAGOON_ENVIRONMENT
• An object type

This would mean that if your prompt said really-long-project-name also-really-long-environment-name variables that you could just write "list", and it would list the variables, and then "add", and it would add a variable to that project/environment.

Describe alternatives you've considered

• Making my bash prompt pick up on some $LAGOON_PROJECT/$LAGOON_ENVIRONMENT variables.
• Having Lagoon pick up on some predefined $LAGOON_PROJECT/$LAGOON_ENVIRONMENT variables. This would also be good to have (whether the suggestion above gets implemented or not).

The issue body names no files, tests, or entry points, so begin by mapping the existing Lagoon CLI command structure. Clarify the REPL scope and context model, then define completion around a prompt showing project, environment, and object type, with commands such as listing and adding variables using that context.