feat: add proxy-config and activate https/http proxy for pixi commands

[gzm55]

This pr add new config keys:

[proxy-config]
https = "http://proxy.com:8080"
http = "http://user:[email protected]"
non-proxy-hosts = [ "domain-1.org", "domain-2.org", ]

Activate the configured proxies at the entrypoint of pixi subcommands, like the https.proxy config keys for git.
With these configs, when developing multiple projects, we can setup different proxies for each projects, and do not need to write the config into pixi.toml [activation] sections.

The common proxy environments such as HTTPS_PROXY and http_proxy can overridden the whole proxy config table, so behaviors of the proxy injection via env are kept.

This pr could help the similar situations in #2757 , #1035, #474, etc.

[baszalmstra]

Awesome PR! However, Im a little unsure about whether setting the variables into the environment is the best solution. I would prefer to be explicit and pass them into reqwest clients where they are used instead.

[gzm55]

@baszalmstra the proxies are now transferred into reqwest::Client, and avoid settting environment vars.

[gzm55]

@baszalmstra proxies for uv are also injected into its inner reqwest client.

pixi run/shell/shell-hook will not inherit the proxies setttings. One needs activate script for proxies settings.

pixi and uv could also execute git fetch command to build the package from source. Because the git has its own proxy config, this pr does not inject proxies into these child processes.

[gzm55]

@baszalmstra is there other suggestion?

[baszalmstra]

@tdejager Could you check the implementation for the uv part?
@ruben-arts Could you check the changes to the config and perhaps the general implementation?

[ruben-arts]

This looks good to me!

[gzm55]

This looks good to me!

@ruben-arts The warning message was updated as you suggested.

[gzm55]

@tdejager Could you check the implementation for the uv part?

@tdejager is there some suggestion about this pr?

[tdejager]

Looks good let's merge!