[Validator] Date range class validator.

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | _NA_
| License       | MIT
| Doc PR        | _NA_

A validator that checks two `DateTime` values in a class and validates that its a valid range (start date is lesser than/equal to end date)

[x] 2.3 API
[] 2.5 API
[] Add `minimum_difference` option? (`1 day`, `1 hour`, `1 month`)