Update schema for php-ext section to add needs-value flag (#12050)

Reference: https://github.com/ThePHPF/pie-design/pull/18

res/composer-schema.json

@@ -324,6 +324,12 @@
                                 "example": "without-xdebug-compression",
                                 "pattern": "^[a-zA-Z0-9][a-zA-Z0-9-_]*$"
                             },
+                            "needs-value": {
+                                "type": "boolean",
+                                "description": "If this is set to true, the flag needs a value (e.g. --with-somelib=<path>), otherwise it is a flag without a value (e.g. --enable-some-feature).",
+                                "example": false,
+                                "default": false
+                            },
                             "description": {
                                 "type": "string",
                                 "description": "The description of what the flag does or means.",