set just flags through environment variables

[gsemet]

Hello

It seems like some flags/options passed through parameter, such as --command-color, cannot be set by environment variable. It could be good to allow setting parameter also from environment variable (some other tickets refered this subject #1829 and #1702).

I would need the following environment variables:

• --dry-run / JUST_DRY_RUN=1
• --quiet / JUST_QUIET=1
• --verbose / JUST_VERBOSE=1
• --color=always / JUST_COLOR=always
• --command-color=green / JUST_COMMAND_COLOR=green
• --justfile justfile / JUST_JUSTFILE=justfile
• --working-directory workdir / JUST_WORKING_DIRECTORY=workdir

For example on Gitlab / Github, colors can be forced enabled by setting environment variable JUST_COLOR=always

Optionally, I would like to have default values for some flags in the justfile itself.

For instance, if the CI variables is defined (in Gitlab), set the JUST_COLOR to alway. And also, always set JUST_COMMAND_COLOR=green no matter the env.

[poliorcetics]

If I get to implement #1829 the way I wish to, this will be fixed that way. I need the clap 4 upgrade in #1865 (I'll resolve the conflicts soon) first though, clap 2 was missing features to work with env variables and defaults