Add activity trigger encode/decode logic for durable function

[Hazhzeng]

Dependency

Azure/azure-functions-python-worker#643

Background

Previously, the Activity Trigger in Python Durable Functions only supports string as return value. Now, we should support JSON serializable Python primitive types.

✔string, int, float, bool, list of string/int/float/bool, dictionary of string/int/float/bool, None
❌set, frozenset, bytes, bytearray, custom type, custom dataclass

[davidmrdavid]

The changes seem reasonable but I'm not an active owner of this repo so I would like someone else to also approve before merging. Also, please review my comment below.