Geo: More design sync failures in staging

Problem

After !39916 (merged), there are still DesignRepositoryUpdatedEvent being processed for Project IDs that should not be processed.

Possible reason

At the moment, I think this is because:

• the MR assumes that DesignRepositoryUpdatedEvent are not created for projects that do not have designs
• project imports create DesignRepositoryUpdatedEvent even when there are no designs https://gitlab.com/gitlab-org/gitlab/blob/v13.3.0-ee/ee/app/models/ee/project_import_state.rb#L63

Possible fixes

1. Implement DesignRepositoryUpdatedEvent#replicable_design? instead of reusing BaseEvent#replicable_project?
2. Check for repos before sending repo update events from import

I think we should actually do both.