Added patch channel API doc for channel banner (#32100)

* Added patch channel API doc for channel banner

* Fixed typo

api/v4/source/channels.yaml

@@ -641,6 +641,8 @@
                   type: string
                   description: Markdown-formatted text to display in the header of the
                     channel
+                banner_info:
+                  $ref: "#/components/schemas/ChannelBanner"
         description: Channel object to be updated
         required: true
       responses:

api/v4/source/definitions.yaml

@@ -4233,6 +4233,18 @@ components:
         value_type:
           type: string
           description: The value type.
+    ChannelBanner:
+      type: object
+      properties:
+        enabled:
+          type: boolean
+          description: enabled indicates whether the channel banner is enabled or not
+        text:
+          type: string
+          description: text is the actual text that renders in the channel banner. Markdown is supported.
+        background_color:
+          type: string
+          description: background_color is the HEX color code for the banner's backgroubd
 externalDocs:
   description: Find out more about Mattermost
   url: 'https://about.mattermost.com'