feat: add env var support while typing

[vitorsss]

Describe your changes

Add minimal support for environment variables while typing.

Type $SOME_ENV_VAR

Related issue/discussion: #621

[dzuelke]

Note that this can already be done when using zsh as the shell with a sequence of Hide, Type "${ENV_VAR_NAME}", Tab, and Show - the shell will then expand the variable (due to the curly braces), correctly escaped:

Set Shell zsh

Type "curl "
Hide
Type "${URL_FROM_ENV}"
Tab
Show

Sleep 2s