Feature/adds activities providers

[spacether]

What was changed

• I added two methods (ActivitiesProvider.get_activities_from_instance + ActivitiesProvider.get_activities_from_cls) to get activities from classes that inherit from ActivitiesProvider
• I added the function get_activities to get activities from a python module
• tests are added of the two new methods and the 1 new function

Why?

These are useful to my code base to extract activities from classes and module

Checklist

1. Closes https://github.com/temporalio/sdk-python/issues/758

2. How was this tested:

• I added tests of the new functionality; they all pass

3. Any docs updates needed? Yes, not sure where docs are generated from, where should this be added?

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