Added support for Cargo http.cainfo

[ranger-ross]

This PR adds support for using a custom CA via the Cargo http.cainfo configuration.

See #612 for more info

[mystor]

I'm not sure we want to add a hard dependency on the full cargo crate. That's a pretty heavy dependency to pull in just to read the cargo config file.

The API of the cargo crate is also quite unstable (as noted in the documentation, in fact the latest version appears to have a different API than the 0.65.0 which you're depending on here).

I'm open to us using cargo HTTP configuration options to configure our reqwest client. Ideally we'd shell out to the cargo subcommand with cargo config get, though that feature is unfortunately still unstable (rust-lang/cargo#9301).

For now, to support this unfortunately I think we'd need to parse the cargo config options independently, rather than relying on the cargo crate to do so. Based on the cargo configuration documentation, the process would roughly be to try to parse TOML from each $ANCESTOR_DIR/.cargo/config or $ANCESTOR_DIR/.cargo/config.toml, then try the next ancestor up, followed by finally checking $CARGO_HOME/config[.toml]. There's also a CARGO_HTTP_CAINFO environment variable which would need to be checked.

[ranger-ross]

Hey @mystor ,
Thanks, thats a totally fair response. (I was also not in love with taking a dependency on cargo)

I updated this PR to remove the dependency on cargo and self implemented the logic for resolving cargo configurations by following the documentation here.

Let me know what you think 👍

[ranger-ross]

Hey there @mystor 👋

I updated this PR to use cargo-config2 instead of Cargo.

[mystor]

I applied some clean-ups and audited the new dependencies. Approving with those changes.

Thanks for the patch!