chore: add MR templates

.gitlab/merge_request_templates/new-package.md

+### Summary
+
+|               |                                        |
+|---------------|----------------------------------------|
+| Package       | <!-- Spack package name -->            |
+| Contact point | <!-- maintainer GitLab handle -->      |
+| KG entry      | <!-- insert link -->                   |
+
+
+### Checks
+
+<!-- please download the EBRAINS Software Quality checklist, fill it and replace the file below -->
+* [ ] Software Quality Checklist: [SQ-Checklist.pdf](https://drive.ebrains.eu/d/6061531326d048308823/files/?p=%2FSQ-Checklist.pdf) (level: <!-- passing, silver, gold -->)
+* [ ] Current maintainer is listed first in `package.py`
+* [ ] No pinned dependency versions
+* [ ] Post-installation tests are defined
\ No newline at end of file

.gitlab/merge_request_templates/new-version.md

+### Summary
+
+|               |                                        |
+|---------------|----------------------------------------|
+| Package       | <!-- Spack package name -->            |
+| Version added | <!-- version number -->                |
+| Contact point | <!-- maintainer GitLab handle -->      |
+| KG entry      | <!-- insert link -->                   |
+
+
+### Checks
+
+<!-- please download the EBRAINS Software Quality checklist, fill it and replace the file below -->
+* [ ] Software Quality Checklist: [SQ-Checklist.pdf](https://drive.ebrains.eu/d/6061531326d048308823/files/?p=%2FSQ-Checklist.pdf) (level: <!-- passing, silver, gold -->)
+* [ ] Current maintainer is listed first in `package.py`
+* [ ] No pinned dependency versions
+* [ ] Post-installation tests are defined
\ No newline at end of file