feat(python): Add custom_repr docs (#11059)

Author: sl0thentr0py

docs/platforms/python/configuration/options.mdx

@@ -219,7 +219,7 @@ When set to `False`, no auto-enabling integrations will be enabled by default, e
 
 Configures whether [default integrations](/platforms/python/integrations/default-integrations/) should be enabled. The default is `True`.
 
-Setting `default_integrations` to `False` disables all default integrations **as well as all auto-enabling integrations**, unless they are specifically added in the `integrations` option, described above. 
+Setting `default_integrations` to `False` disables all default integrations **as well as all auto-enabling integrations**, unless they are specifically added in the `integrations` option, described above.
 
 
 ## Hooks
@@ -386,3 +386,23 @@ The threshold in milliseconds for adding the source location to database queries
 Default is `100` ms.
 
 </ConfigKey>
+
+<ConfigKey name="custom-repr">
+
+A custom [repr](https://docs.python.org/3/library/functions.html#repr) function to run while serializing an object. Use this to control how your custom objects and classes are visible in Sentry.
+
+Return a string for that repr value to be used or `None` to continue serializing how Sentry would have done it anyway.
+
+```python
+def custom_repr(obj):
+    if isinstance(obj, MyCustomClass):
+        return "<MyCustomClass>"
+    else
+        return None
+
+sentry_sdk.init(custom_repr=custom_repr)
+```
+
+Default is `None`.
+
+</ConfigKey>