(feat): add GitLab MR template for contributors

gitlab/merge_request_templates/Contributor.md

+## Community contributors
+
+Thanks for your interest in the site! To ensure your changes are merged swiftly, please make sure you have done the following before submitting your merge request:
+
+- Sign the [Contributor License Agreement](https://powerforms.docusign.net/e9c0907f-7056-403e-9972-0caad4ced5b6?env=na3-eu1)
+- Read the [Contributing guide](https://developers.minds.com/docs/contributing/contributing/)
+- Understand [how we use GitLab](https://developers.minds.com/docs/guides/git/)
+
+When you're ready to submit, you can delete this template (except for the labelling Quick Action shortcut below) and replace it with a detailed description of your merge request.
+
+---
+
+{- Leave this here -}
+
+/label ~Product::Docs ~MR::"Awaiting Review" ~Platform::Browser ~Priority::"2 - Normal" ~Type::Chore