Add release team to cargo crate

[ChristianMurphy]

Initial checklist

• I read the support docs
• I read the contributing guide
• I agree to follow the code of conduct
• I searched issues and couldn’t find anything (or linked relevant results below)

Problem

@mdx-js/releasers currently are not owners on the https://crates.io/crates/mdx crate.
Meaning the release team, is unable to do releases.

If the release team had access, the mdx crate (https://crates.io/crates/mdx) and mdxjs (https://crates.io/crates/mdxjs) crate could probably merge back together.

Solution

Add the release team as owners on crates.io
https://doc.rust-lang.org/cargo/commands/cargo-owner.html

Alternatives

Mark the mdx crate as deprecated