[FEATURE] Flag for `exo env` to show origin of variables

[brandonbloom]

Is your feature request related to a problem? Please describe.

exo env prints variables in .env file format, but that loses some potentially important debugging information that the GUI already supports: The origin of each variable!

Describe the solution you'd like

Add a flag to print with a tabwriter that prints three columns: name, value, origin. Ideally with a header column too, prefixed by a #.

Suggested flag: -v and --verbose.

Describe alternatives you've considered

Could include # comments before each variable and stay in env format, but we'd still want this behind a flag.

Additional context

cc @finnigantime