Add --cargo-arg option for arguments to pass through to cargo

[danakj]

Some projects may require additional arguments in the cargo metadata command in order to parse their Cargo.toml. For example Chromium requires -Zbindeps as it uses the feature for a dependency on cxxbridge-cmd. This allows such projects to use cargo vet --cargo-arg=<STUFF> in order to add one or more arguments to the cargo metadata command line.

[danakj]

Not sure if there's an expectation for tests here, but locally I did the following:

% cargo run -- vet --cargo-arg=-Zbindeps --verbose info
    Finished dev [unoptimized + debuginfo] target(s) in 0.14s
     Running `target/debug/cargo-vet vet --cargo-arg=-Zbindeps --verbose info`
 INFO Running: Command {
    program: "/home/danakj/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/cargo",
    args: [
        "/home/danakj/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/cargo",
        "metadata",
        "--format-version",
        "1",
        "--all-features",
        "--locked",
        "--color=always",
        "-Zbindeps",            <---------------- added here
    ],
    create_pidfd: false,
}
 INFO Final Metadata Config: 
...

[bholley]

Thanks for the patch! @mystor can you review?

[danakj]

Oh I see there are tests for the help markdown, I will update those.

[mystor]

While it'd be nice to have tests for this, it's a fairly niche feature, and is useful for something somewhat niche, so I think we can get away without functionality tests for this change.

[danakj]

Thanks for the quick review!