Refactor github requests to use traits whenever rust adds support for traits with async functions

[KevinCLydon]

The different types of github requests in the manager::github package would make more sense to implement using traits. However, rust does not currently support traits with async functions. There is a crate that adds support, but it's finicky in ways that make it difficult to use for our use case. Whenever rust officially adds support for traits with async functions, we should probably refactor the github requests to use a trait.