Create pull_request_template.md

Author: egil

.github/PULL_REQUEST_TEMPLATE/pull_request_template.md

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+## Pull request description
+<!--- 
+    Describe the changes here and motiviations behind them, if it is not obvious
+    from the related issues. Does it have new features, breaking changes, etc. 
+-->
+
+### PR meta checklist
+- [ ] Pull request is targeting at `DEV` branch.
+- [ ] Pull request is linked to all related issues, if any.
+- [ ] I have read the _CONTRIBUTING_ document.
+
+### Content checklist
+- [ ] My code follows the code style of this project and AspNetCore coding guidelines.
+- [ ] My change requires a change to the documentation.
+  - [ ] I have updated the documentation accordingly.
+- [ ] I have updated the appropriate sub section in the _CHANGELOG.md_.
+- [ ] I have added, updated or removed tests to according to my changes.
+  - [ ] All tests passed.