[CLOUD-78] authz: re-enable user-centric perms syncing for user code host conns
Created by: unknwon
For small orgs EA, we need to (re-)enable user-centric permissions syncing based on user code host connections because login connections does not have repo
scope granted (which is required to access GitHub repo APIs).
This implies that:
- Users need to connect personal code host connection in order to see private repositories added to their organizations on Sourcegraph.
- When users go through OAuth flow, they need to grant access from the GitHub organization they're intended to add repositories to Sourcegraph.
This PR adds back the code that is functionally equivalent to https://github.com/sourcegraph/sourcegraph/pull/23018.
Jira: CLOUD-78