Enable Mirrored Registry Instead of crates.io

[mireysia]

Problem

In airgapped or highly secured environments, direct access to crates.io is not feasible. Instead, users rely on sanitized, mirrored registries for dependency resolution. Currently, Reindeer can use cargo vendor --respect-source-config to target a custom registry, but this requires defining a static .cargo/config.toml file with the desired source configurations.

Proposed solution

Introduce a new section in the reindeer.toml file to define different registry config. This is eliminates the need for modifying project specific .cargo/config.toml files

[source]
name = "mirrors"
registry = "https://mirrors.tuna.tsinghua.edu.cn/crates.io-index/"

Update cargo vendor command

cargo vendor --respect-source-config \
 --config 'source.crates-io.replace-with="mirror"' \
 --config 'source.mirror.registry="sparse+https://mirrors.tuna.tsinghua.edu.cn/crates.io-index/"'