changecontrol.v1: Add changecontrol validations proto

Adds ChangeControlValidationStatus and ChangeControlValidationDetail
to provide status and details for older designed config or image
warning. This can be extended for future warnings or validations.
Also adds OverrideReason to override the warning.

[GENERATED_COMMIT]

Change-Id: I7a483971c709d4e6db4f29ae57224b0736ded548

Author: Arista Jenkins