docs: add breaking change entry

Fixes https://github.com/emqx/emqx/pull/13420#issuecomment-2213957235

changes/ee/breaking-13420.en.md

@@ -0,0 +1 @@
+Added a schema validation that prevents configuring an empty set of topic filters for a Schema Validation.  Any such configurations will have to define at least one topic filter to be valid.  Such configurations, though, are probably very rare, as a Schema Validation with empty topics is essentially the same as having no validation at all.