Could we have an "registries" option for rust-analysis?

[bioinformatist]

By default, Zed tries to download the rust-analysis binary from GitHub releases.
As an user in China, the GitHub connection may be sometimes blocked by the GFW. So it would be great if we can set other registries for rust-analysis binary (it's been maintained by some universities in China, such as this one).

Should it be a new feature? I'm glad to implement it. And I think it'll make Zed more polular in China, which could be a tremendous market 😃