Add issue and merge request templates

.gitlab/issue_templates/template.md

+## Description
+
+<!--
+Please describe shortly what this merge request is doing and why
+it is needed. If there is an related issue, please mention it here.
+-->
+
+## Checklist
+
+<!--
+Please make sure to go over all points on the checklist and
+mark them as checked.
+-->
+
+- [ ] I made sure that the source files are formatted properly.
+- [ ] I added my changes to the changelog (`CHANGELOG.md`)
+- [ ] I updated the documentation.
+
+<!--
+If the pull request adds new content, please check the points
+below. Otherwise remove the following lines.
+-->
+
+- [ ] I added a test for the new feature.

.gitlab/merge_request_templates/template.md

+## Description
+
+<!--
+Please describe the problem/feature request. Please also describe what you want
+to achieve.
+--->
+
+### Environment
+
+<!--
+Please provide information about the operating system and relevant versions of
+the software.
+
+Example:
+Ubuntu 20.04 LTS, preCICE 2.3.0, DuMuX 3.4, DuMuX-preCICE 0.1
+--->
+
+## Steps to reproduce
+
+<!-- Please describe the steps one has to execture to reproduce the problem. --->
+
+### Expected behavior
+
+<!-- What outcome did you expect? --->
+
+### Actual behavior
+
+<!-- What was the actual outcome? --->

CHANGELOG.md

@@ -2,6 +2,7 @@
 
 ## Not released yet
 
+- 2022-01-25: Added [description templates](https://docs.gitlab.com/ee/user/project/description_templates.html) for merge requests and issues.
 - 2022-01-12: The repository has been restructured. The main changes are:
 
   - The adapter is now called `CouplingAdapter` and resides in `dumux-precice/`. The build process has been adapted accordingly.