Use $EDITOR as default editor if set #1527

Is your feature request related to a problem? Please describe.
I've set $EDITOR to helix.
Editing a role in REPL mode still opens nano instead.

Describe the solution you'd like
aichat uses $EDITOR (if not empty), if nothing is configured in config.yaml

Describe alternatives you've considered
As a workaround, I've set editor: helix manually in config.yaml.