Migrate example submissions to a form (#931)

- Don't show in changelog

Author: D8H

.github/ISSUE_TEMPLATE/new-example.md

@@ -0,0 +1,57 @@
+name: ✨New example
+about: Submit a new example to be added to the repository
+title: 'New example:  <title>'
+labels: ['✨ New example']
+body:
+  - type: markdown
+    attributes:
+      value: '# Example submission'
+  - type: textarea
+    id: description
+    attributes:
+      label: Description
+      description: A clear and concise description of what the example is, how useful it is.
+      placeholder: This example shows how to...
+  - type: checkboxes
+    id: checklist
+    attributes:
+      label: Checklist
+      description: Make sure you have done all of this before submitting!
+      options:
+        - label: "I've followed all of [the best practices](https://wiki.gdevelop.io/gdevelop5/community/guide-for-submitting-an-example)."
+          required: true
+        - label: My game has a proper name in the game properties.
+          required: true
+        - label: My game package name begins with `com.example.`.
+          required: true
+        - label: My game has all events unfolded.
+          required: true
+        - label: I've added myself as the author in the game properties.
+          required: true
+        - label: I've included a file called "README.md" with a description in proper English, explaining what this example is doing.
+          required: true
+        - label: I confirm that this game and all of its resources can be integrated to this GitHub repository, distributed and MIT licensed.
+          required: true
+        - label: I've cleaned unused resources.
+          required: true
+  - type: textarea
+    id: example
+    attributes:
+      label: Game project folder
+      description: Please drag into this text field a zip file containing your game project folder and all its resources (images, sounds, etc...). **DO NOT PUT A LINK TO AN EXTERNAL SERVICE LIKE GOOGLE DRIVE!**
+      placeholder: '[MyExample.zip]()'
+    validations:
+      required: true
+  - type: textarea
+    id: preview
+    attributes:
+      label: Game preview
+      description: You can add a few screenshots of your game and a link to play it to show how cool your example is.
+      placeholder: 'Try my game on gd.games...'
+    validations:
+      required: false
+  - type: markdown
+    attributes:
+      value: |
+        If your game is high quality and useful, it will be added to the list of GDevelop community examples.
+        Thanks for contributing to GDevelop! 🙌