Handling custom exception type from activities

I would like to understand if it is possible to handle custom exception type (from activities) inside the orchestrator function.

E.g.:

Activity
```python
raise MyException(custom_data={...})
```
Orchestrator:
```python
try:
res = yield context.call_activity("Activity", data)
except MyException as me:
print(me.custom_data)
```

The actual behaviour is that in the orchestrator function I only get the generic Exception type and I cannot differentiate the handle logic based on custom_data.

Start by reproducing the Activity raising MyException and the orchestrator calling context.call_activity, then trace how the activity exception reaches the orchestrator. Done means determining whether the custom exception type and custom_data can be preserved for differentiated handling, and documenting or implementing the required behavior.

Written by the indexing model from the issue text.