docs: Add JSON credentials blob example (#2915)

website/content/docs/concepts/domain-model/credentials.mdx

@@ -46,8 +46,28 @@ The following credential types are supported in Boundary:
 ### JSON
 
 As of Boundary 0.11.0, you can provide credentials using a JSON blob.
-There is no required structure for the JSON blob, other than it must be a key value map.
 JSON credentials are only brokered to users that connect to machines.
+There is no required structure for the JSON blob, other than it must be a key value map.
+Refer to the example below:
+
+<CodeBlockConfig heading="JSON credentials blob example">
+
+```JSON
+{
+  "type": "service_account",
+  "project_id": "",
+  "private_key_id": "",
+  "private_key": "-----BEGIN PRIVATE KEY----------END PRIVATE KEY-----\n",
+  "client_email": "",
+  "client_id": "",
+  "auth_uri": "https://accounts.google.com/o/oauth2/auth",
+  "token_uri": "https://oauth2.googleapis.com/token",
+  "auth_provider_x509_cert_url": "https://www.googleapis.com/oauth2/v1/certs",
+  "client_x509_cert_url": ""
+}
+```
+
+</CodeBlockConfig>
 
 ## Referenced by