fix: wrong type of payload and headers in MessageExample

According to JSON Schema headers and payload properties may be of any type

#3530

markdown/docs/reference/specification/v3.0.0.md

@@ -1335,8 +1335,8 @@ Message Example Object represents an example of a [Message Object](#messageObjec
 
 Field Name | Type | Description
 ---|:---:|---
-<a name="messageExampleObjectHeaders"></a>headers | `Map[string, any]` | The value of this field MUST validate against the [Message Object's headers](#messageObjectHeaders) field.
-<a name="messageExampleObjectPayload"></a>payload | `Map[string, any]` | The value of this field MUST validate against the [Message Object's payload](#messageObjectPayload) field.
+<a name="messageExampleObjectHeaders"></a>headers | `any` | The value of this field MUST validate against the [Message Object's headers](#messageObjectHeaders) field.
+<a name="messageExampleObjectPayload"></a>payload | `any` | The value of this field MUST validate against the [Message Object's payload](#messageObjectPayload) field.
 <a name="messageExampleObjectName"></a>name | `string` | A machine-friendly name.
 <a name="messageExampleObjectSummary"></a>summary | `string` |  A short summary of what the example is about.
 
@@ -2585,4 +2585,4 @@ binary | `string` | `binary` | any sequence of octets
 boolean | `boolean` | | |
 date | `string` | `date` | As defined by `full-date` - [RFC3339](https://www.rfc-editor.org/rfc/rfc3339.html#section-5.6)
 dateTime | `string` | `date-time` | As defined by `date-time` - [RFC3339](https://www.rfc-editor.org/rfc/rfc3339.html#section-5.6)
-password | `string` | `password` | Used to hint UIs the input needs to be obscured.
+password | `string` | `password` | Used to hint UIs the input needs to be obscured.