feat(cargo): support private crate

[vmaerten]

Changes

For the Cargo manager, I've enabled by default net.git-fetch-with-cli.
I also enable hostRule for passing token to pull private crate (like it's done for Golang)

Context

Closes #20059
Cargo, in Renovate, could not pull private crate when updating artifacts.

Documentation (please check one with an [x])

• I have updated the documentation, or
• No documentation update is required

How I've tested my work (please select one)

I have verified these changes via:

• Code inspection only, or
• Newly added/modified unit tests, or
• No unit tests but ran on a real repository, or
• Both unit tests + ran on a real repository

I've updated the snapshot to see the new Cargo config, and I tested it locally pointing to a repo with a private crate.

It's my first PR, I hope I did not miss something.

[secustor]

Add an entry in in cargo/index.md that this is happening.

[vmaerten]

Thanks for your review!
I've updated the doc in cargo/readme.md, following the same convention as for golang (gomod/readme.md)
I've also added 3 tests to ensure that env variable are applied

[HonkingGoose]

First pass review, needs more work after.

[vmaerten]

@HonkingGoose I've applied your suggestions.
I also tried to rephase the self hosted part.

[HonkingGoose]

I'm happy with the docs, but I want a maintainer to review the left and right side of the Markdown diff. I suspect we're accidentally dropping some information.

[renovate-release]

🎉 This PR is included in version 37.5.0 🎉

The release is available on:

• GitHub release
• 37.5.0

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