Add issue template for refactorings

.gitlab/issue_templates/Refactoring.md

+## Summary
+
+<!--
+Please briefly describe what part of the code base needs to be refactored.
+-->
+
+## Improvements
+
+<!--
+Explain the benefits of refactoring this code.
+See also https://about.gitlab.com/handbook/values/index.html#say-why-not-just-what
+-->
+
+## Risks
+
+<!--
+Please list features that can break because of this refactoring and how you intend to solve that.
+-->
+
+## Involved components
+
+<!--
+List files or directories that will be changed by the refactoring.
+-->
+
+## Optional: Intended side effects
+
+<!--
+If the refactoring involves changes apart from the main improvements (such as a better UI), list them here.
+It may be a good idea to create separate issues and link them here.
+-->
+
+
+## Optional: Missing test coverage
+
+<!--
+If you are aware of tests that need to be written or adjusted apart from unit tests for the changed components,
+please list them here.
+-->
+
+/label ~backstage