Implement `repos.list` replacement (!1700) · Merge requests · Administrator / sourcegraph

Created by: tsenart

Checklist:

Add "OtherExternalServiceConnection" type to site.schema.json
Document changes.
Update Changelog.
Add code to https://github.com/sourcegraph/sourcegraph/tree/master/cmd/repo-updater/repos to fetch repos for these other connections.
Fix JSON schema Monaco editor validation (it doesn't seem to support dependencies)
Write a test plan

Closes #1550

Implement `repos.list` replacement