Feature Request: Support domain specification

[dsprayberry]

A Stitch user requested the ability to be able to specify an internal Github endpoint to pull data from, which was not functioning when populating the repository name field of the integration. eg, "github.singer.com" rather than simply singer-io, where entering singer was non-functional.

They received 401 errors during extraction without much logging surrounding those auth errors, and the extractions eventually ended with schema mismatch (due to no values being returned).