Add an example with a simple tile map editor

[D8H]

Require:

• Allow to edit external tile maps during runtime 4ian/GDevelop#8830

[github-actions]

Preview the game(s) changed or added in this Pull Request

• https://editor.gdevelop.io?project=https://raw.githubusercontent.com/GDevelopApp/GDevelop-examples/tile-map/examples/dynamic-tilemap/Dynamic
• https://editor.gdevelop.io?project=https://raw.githubusercontent.com/GDevelopApp/GDevelop-examples/tile-map/tile
• https://editor.gdevelop.io?project=https://raw.githubusercontent.com/GDevelopApp/GDevelop-examples/tile-map/map.json
• https://editor.gdevelop.io?project=https://raw.githubusercontent.com/GDevelopApp/GDevelop-examples/tile-map/examples/dynamic-tilemap/assets/ExternalTileMap.json
• https://editor.gdevelop.io?project=https://raw.githubusercontent.com/GDevelopApp/GDevelop-examples/tile-map/examples/platformer-with-tilemap/platformer-with-tilemap.json

---

This is an automatic message displaying links to the games in this PR - double check the JSON in case of doubt.