Added changelog

CHANGELOG.md

+<!--
+Types of changes:
+  - Added: for new features.
+  - Changed: for changes in existing functionality.
+  - Deprecated: for soon-to-be removed features.
+  - Removed: for now removed features.
+  - Fixed: for any bug fixes.
+  - Security: in case of vulnerabilities.
+-->
+
+# Event-Payload Changelog
+
+* The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
+* If available, include a ticket number in format `(planning#XXXX)`.
+
+
+## [1.1.0]
+
+### Changed
+
+ - `$schema` von einem Enum in eine RegEx geändert `(planning#608)`
+
+## [1.0.0]
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