Fix item parameter for custom field options (#2572)

* fix defaultValue set at the wrong place 

the defaultValue property must be placed in the item object and can be type string or boolean

* update description for item parameter defaultValue

* remove whitespace

Author: raphaeldas

docusaurus/docs/dev-docs/custom-fields.md

@@ -281,6 +281,7 @@ Each object in the `items` array can contain the following parameters:
 | `description`   | Description of the input to use in the Content-type Builder        | [`IntlObject`](https://formatjs.io/docs/react-intl/) |
 | `intlLabel`     | Translation for the label of the input                             | [`IntlObject`](https://formatjs.io/docs/react-intl/) |
 | `type`          | Type of the input (e.g., `select`, `checkbox`)                     | `String`                                             |
+| `defaultValue`  | Set the default value for the item                                 | `String` | `boolean`                                 |
 
 <details>
 <summary>Example: Declaring options for an example "color" custom field:</summary>
@@ -322,12 +323,11 @@ export default {
                 },
                 name: "options.format",
                 type: "select",
-                value: "hex", // option selected by default
+                defaultValue: "hex", // option selected by default
                 options: [
                   // List all available "Color format" options
                   {
                     key: "hex",
-                    defaultValue: "hex",
                     value: "hex",
                     metadatas: {
                       intlLabel: {