docs: Adding docs for default values on Exception fields. (#156)

* docs: Adding docs for default values on Exception fields

* docs: Default values for Exceptions docs improvement

docs/06-concepts/04-exceptions.md

@@ -50,3 +50,25 @@ catch(e) {
   print('Something else went wrong.');
 }
 ```
+
+### Default Values in Exceptions
+
+Serverpod allows you to specify default values for fields in exceptions, similar to how it's done in models using the `default` and `defaultModel` keywords. If you're unfamiliar with how these keywords work, you can refer to the [Default Values](models#default-values) section in the [Working with Models](models) documentation.
+
+:::info
+Since exceptions are not persisted in the database, the `defaultPersist` keyword is not supported. If both `default` and `defaultModel` are specified, `defaultModel` will always take precedence, making it unnecessary to use both.
+:::
+
+**Example:**
+
+```yaml
+exception: MyException
+fields:
+  message: String, default="An error occurred"
+  errorCode: int, default=1001
+```
+
+In this example:
+
+- The `message` field will default to `"An error occurred"` if not provided.
+- The `errorCode` field will default to `1001`.