Add "provider" attribute to @GroupSequence inspired by the Hibernate's @GroupSequenceProvider

At the moment there is no mechanism to define the group sequence validation at runtime. Hibernate Validator has its own mechanism, through [@GroupSequenceProvider](https://docs.jboss.org/hibernate/stable/validator/reference/en-US/html_single/#_groupsequenceprovider) annotation and DefaultGroupSequenceProvider interface.

Inspired by the Hibernate's solution, my suggestion is to add the attribute "provider" to the @GroupSequence annotation which expects a reference to a class that implements the interface "GroupSequenceProvider".

More info: [Hibernate Validator docs](https://docs.jboss.org/hibernate/stable/validator/reference/en-US/html_single/#_groupsequenceprovider).

Start by reading the @GroupSequence annotation and the linked Hibernate Validator documentation for @GroupSequenceProvider and DefaultGroupSequenceProvider. Determine how a provider attribute and GroupSequenceProvider interface would fit the validation specification, including the expected runtime behavior. Done means the proposed API and its semantics are specified consistently.

Written by the indexing model from the issue text.