Add 5.x changelog

doc/changelogs/CHANGELOG-5.x.md

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+Netgen Tags Bundle 5.x changelog
+================================
+
+5.0.0 (06.05.2022)
+------------------
+
+Since 5.0 is a new major release, there were a number of breaking changes, so be sure to read [upgrade instructions](UPGRADE.md#upgrade-from-40-to-50).
+
+The following lists only the most important changes from version 4.0 to version 5.0:
+
+* Minimum supported version of PHP is now PHP 7.4 or 8.0+
+* Minimum supported version of Ibexa Platform is now 4.0
+* Service name for Tags service has been renamed to `netgen_tags.api.service.tags` (old name is kept for BC) 
+* The codebase has been modernized across the board:
+    - Property typehints have been added to all code