Checking the subscriber limit has nothing to do with the newsletter
itself, so it makes more sense to continue to perform that check as
needed elsewhere in the codebase.
MAILPOET-4236
- Rename validator to newsletterValidator for clarity
- Add validation for ALC content
- Refactor tests to use data factory for consistency and to avoid
validation issues
- Add separate tests for NewsletterValidator service
- Add test helper for retrieving service with private properties
overridden by name
[MAILPOET-4236]
