Public code on Cloud release (Milestone 3)

Created by: ryanslade

This issue tracks the soft release of public code on sourcegraph.com which we refer to as milestone 3 in product board

Blocking Issues

• repos: make GitLab repo syncing support OAuth token
• SetExternalServiceRepos GraphQL query takes a long time
• UserRepositories GraphQL query takes a long time
• No entrypoint for adding public code without first adding a code host
• Add GitLab Auth provider for dotcom #16745 (closed)
• Public repos are not listed in UserSettingsRepositoryPage if the user doesn't also have repos added via a code host.
• GraphQL DeleteExternalService is slow
• When adding invalid tokens (think bla-bla-42) for GitHub code host, backend doesn't report warnings/errors #18740 (closed)

FE

• Sort selected repositories at top of list in subsequent loads of "Manage repos" view #18780 (closed)
• In "Manage repos" view, searching while viewing paginated page other the the first is broken. #19367 (closed)
• Some UI "jumps" when the scroll is introduced to the repo view https://github.com/sourcegraph/sourcegraph/issues/19371

Steps for release

• Enable for all current sourcegraph employees
• Announce in Slack
• Handle internal feedback (Add issues here once we have them)
• Enable for all users by removing code paths that check for the feature. This should be enabled for sourcegraph.com only