Refine Query by Example string matching to call out store-specific limitations

[kmeyer-mbs]

Criteria API doesn't support regular expressions.

Related tickets spring-data-jpa 1295, spring-data-jpa 3391

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[mp911de]

We need to refine our documentation, however, we cannot list each store rules individually as we would end up with a huge matrix providing details for unrelated stores (i.e. the MongoDB documentation or Redis documentation would talk about JPA specifics). I'm going to tweak the wording accordingly.