Add Mongoid::Relations::Cascading::Restrict.

Fixes #1354. This is only a simple implementation and it doesn't
consider embedded relations as pointed out here:
https://github.com/mongoid/mongoid/issues/1354#issuecomment-2887859.
Add DeleteRestriction error.

Conflicts:

	lib/config/locales/en.yml
	lib/mongoid/errors.rb
Merge pull request #4 from ErisExchange/kurt-add_support_for_depent_restrict_relation