Add env variable to configure locked, frozen and color

[hadim]

See #714 for context.

In short, it adds:

• PIXI_COLOR to configure --color
• PIXI_LOCKED to configure --locked
• PIXI_FROZEN to configure --frozen

I could not find a way to configure --quiet and --verbose since the Verbosity struct belongs to clap_verbosity_flag.

I went the easy way for the name of the env variables, but please let me know if you prefer something else.

---

TODO:

• write doc for the new env variables.

[ruben-arts]

This looks good to me, please describe it in the docs.

[hadim]

I added the doc.

I tried to tweak args.verbose to add env variable support to it, but args.verbose.verbose and args.verbose.quiet are private, so I can't modify those without modifying clap-verbosity-flag itself.

[hadim]

I tried to tweak args.verbose to add env variable support to it, but args.verbose.verbose and args.verbose.quiet are private, so I can't modify those without modifying clap-verbosity-flag itself.

xref with clap-rs/clap-verbosity-flag#53 (comment)

[wolfv]

For PIXI_COLOR it might be good to also respect the standard variables: https://github.com/prefix-dev/rattler-build/blob/d502a2bf4eb4b46a2b38015f74d232177e7dda44/src/env_vars.rs#L195-L208

CLICOLOR_FORCE or FORCE_COLOR, and NO_COLOR

https://docs.conan.io/2/reference/environment.html#terminal-color-variables
https://force-color.org/
https://bixense.com/clicolors/

Not sure which one is more widely adopted though.

[ruben-arts]

Thanks again @hadim