Add default MR template

.gitlab/merge_request_templates/Default.md

+# Summary
+
+    Insert a meaningful description for this merge request here.  What is the
+    new/changed behavior? Which bug has been fixed? Are there related Issues?
+
+# Focus
+
+    Point the reviewer to the core of the code change. Where should they start
+    reading? What should they focus on (e.g. security, performance,
+    maintainability, user-friendliness, compliance with the specs, finding more
+    corner cases, concrete questions)?
+
+# Test Environment
+
+    How to set up a test environment for manual testing?
+
+# Check List for the Author
+
+Please, prepare your MR for a review. Be sure to write a summary and a
+focus and create gitlab comments for the reviewer. They should guide the
+reviewer through the changes, explain your changes and also point out open
+questions. For further good practices have a look at [our review
+guidelines](https://gitlab.com/caosdb/caosdb/-/blob/dev/REVIEW_GUIDELINES.md)
+
+- [ ] All automated tests pass
+- [ ] Reference related Issues
+- [ ] Up-to-date CHANGELOG.md
+- [ ] Annotations in code (Gitlab comments)
+  - Intent of new code
+  - Problems with old code
+  - Why this implementation?
+
+
+# Check List for the Reviewer
+
+
+- [ ] I understand the intent of this MR
+- [ ] All automated tests pass
+- [ ] Up-to-date CHANGELOG.md
+- [ ] The test environment setup works and the intended behavior is
+  reproducible in the test environment
+- [ ] In-code documentation and comments are up-to-date.
+- [ ] Check: Are there spezifications? Are they satisfied?
+
+For further good practices have a look at [our review guidelines](https://gitlab.com/caosdb/caosdb/-/blob/dev/REVIEW_GUIDELINES.md).
+
+
+/assign me