Add async-graphql rust crate

[sunli829]

Async-graphql is a GraphQL server library that fully supports async/await and is easy to use.

Repo: https://github.com/async-graphql/async-graphql
Examples: https://github.com/async-graphql/examples

[carolstran]

👋🏼 Thanks for taking the time to open this pull request! We're currently re-evaluating how we handle contributions to this Code page and pausing any changes until after those decisions are made. So I'm going to mark this PR as On hold and if you have any thoughts on this topic, it'd be great if you could voice them in #911

[carolstran]

Hey hey 👋🏼 the Gatsby migration (#938) has been merged so now we can update the content again. Could you please resolve the conflicts on your branch?

[sunli829]

Thanks, I have resolved the conflict.

[carolstran]

Looks good to me! Tagging @orta to check the formatting because I'm not sure how it should look when there are one longer example and one listed library.

[orta]

I'm going to close this PR as these changes were manually merged upstream by @ardatan in #936 - thanks for updating the list.

Note: We now have markdown files which allow for longer descriptions on the new code page: https://graphql.org/code/ - so it'd be awesome if you added some code samples etc to help any project on the page shine.