technical-debt: added changelog for current snapshot version

CHANGELOG.md

+# Changelog
+
+## [1.9.0] - 2020-10-30
+
+* removed Camunda BPMN dependency
+* updated Spring Boot framework to version 2.3.4.RELEASE
+* updated teis-gradle-plugin version to latest which contains different Gradle dependency configuration sets (functionalities) and therefore Gradle configuration was stripped down from microservice configuration
+* updated Gradle Wrapper to version 5.6.4
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