insights: Add no-op migrator for insights oob migration
Created by: CristinaBirkel
Closes https://github.com/sourcegraph/sourcegraph/issues/39106
Description
We weren't registering our oob migration if code insights was disabled. This registers a no-op migrator that will always return 100% complete. This allows customers (without code insights) to upgrade past the point of this migration's deprecation (which will be the next version) without needing manual intervention.
Test plan
I tested this on a single docker deployment and verified that the migration completed to 100%. You could also verify this locally by disabling code insights.