Publishes GitHub templates to simplify issue reporting and contributions

.github/ISSUE_TEMPLATE/change_request.md

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+---
+name: Change request
+about: Suggest a change for Thunderbird User.JS
+title: "[RFC] "
+labels: 'enhancement'
+assignees: ''
+
+---
+
+**Is your feature request related to a problem? Please describe.**
+<!-- A clear and concise description of what the problem is. Ex. I'm always frustrated when [...] -->
+
+
+**List the concerned preferences**
+<!-- A clear and concise list of the preferences you want to add/remove/change. -->
+
+
+**Describe alternatives you've considered**
+<!-- A clear and concise description of any alternative solutions or features you've considered. -->
+
+
+**Additional context**
+<!-- Add any other context (Thunderbird version, OS, etc.) or screenshots about the feature request here. -->
+
+
+**Checklist**
+<!--- Put an `X` in all the boxes that apply : -->
+- [ ] I know `thunderbird user.js` is a **template** and personal preferences should be stored elsewhere ;
+- [ ] The change I want to propose should globally improve the `usability / ( privacy + security + anti-fingerprinting )` ratio ;
+- [ ] I agree that subsequent modifications to my change scope may occur in the future.