repo-updater: Return all ExternalServices
Created by: keegancsmith
Our enabled migration relies on all external services being returned. However, it had two flaws:
- It did type assertions against concrete types. We now wrap our concrete source types in an observable layer, causing the assertions to fail.
- It only handled GitHub
After this commit the enabled migration should run against all sources we support as well as succeed outside of unit tests.
Test plan: Tested via launch.sh from a DB snapshot of a 3.2 release.
Fixes https://github.com/sourcegraph/sourcegraph/issues/3450