graphqlbackend: Gracefully handle some code host failures for AffiliatedRepos

Created by: ryanslade

This change allows us to gracefully handle failures in only some of the code hosts when listing affiliated repos.

The resolver type and file were also renamed to make them more consistent.

Closes: https://github.com/sourcegraph/sourcegraph/issues/20934

Note that the final test is failing which I'll look into tomorrow. It's most likely something to do with error formatting.