[Book][Validation] configuration examples for the GroupSequenceProvider
feature #3803 [Book][Validation] configuration examples for the GroupSequenceProvider (xabbuh)

This PR was merged into the 2.3 branch.

Discussion
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[Book][Validation] configuration examples for the GroupSequenceProvider

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?     | no
| Applies to    | all
| Fixed tickets |

This pull requests adds examples in different formats for the GroupSequenceProvider feature of the Validator component (it's the completion of #3369).

Commits
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bfd2af4 [Book][Validation] configuration examples for the GroupSequenceProvider