Release v21.10.0

Added

• The name of the violated constraint on a validation result, so a client can tell one constraint rejection from another without matching on the message text (#2487)
• ShouldHaveConstraintViolationFor for asserting a command result names a given constraint, matching the assertion already available against a raw append (#2487)

Fixed

• A client-composed validation failure no longer loses its reason, which had reported every such result as an authored rule (#2487)