[Composer] Add suggested extensions

composer.json

@@ -77,6 +77,12 @@
 		"npm-asset/textcomplete": "^0.18.2",
 		"npm-asset/typeahead.js": "^0.11.1"
 	},
+	"suggest": {
+		"ext-imagick": "For faster image processing",
+		"ext-redis": "To use Redis as a locking or caching provider",
+		"ext-pdo": "To use PDO as a database driver, has priority over mysqli unless database.disable_pdo is set",
+		"ext-mysqli": "To use mysqli as a databse driver"
+	},
 	"repositories": [
 		{
 			"type": "vcs",