Add extra check about existing and new $contractual

[mferrera]

Removing a contractual item should be an exceptionally rare occurrence. We should add an additional check around the contractual items.

If existing contractual is not a subset of the new contractual:

• It should flag and warn, at minimum, from update-schemas.
  • Maybe this requires an additional flag to force, like --force-contractual (in addition to existing --force)
• A test should fail (?) (this may not be practical for CI)