Add some more details to the MR template

.gitlab/merge_request_templates/MR.md

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+<!-- Please describe your changes here in a concise manner -->
+
+-----------------------------------------------------------------------------
+
+- [ ] I ran `cargo fmt --all`, `cargo test --workspace` and `cargo clippy`
+- [ ] I agree to release my code and all other changes of this MR under the Apache-2.0 license
+