Add required metadata to the new default wallpaper for KDE Plasma (MR 29)

"required" is a bit much, but it's great to give credit where credit is
due on the right spots.

wallpapers/2024/meadow/metadata.json

+{
+	"KPlugin": {
+		"Authors": [
+			{
+				"Email": "dikasetyaprayogi@gmail.com",
+				"Name": "Dika Setya"
+			}
+		],
+		"Id": "Meadow",
+		"License": "CC-BY-SA-4.0",
+		"Name": "Meadow"
+	}
+}