RNA API for creating & removing channelbags, as well as a path function
to construct RNA paths for channelbags.
```python
action = bpy.data.actions.new('TestAction')
slot = action.slots.new()
slot.name = 'OBTest'
layer = action.layers.new(name="Layer")
strip = layer.strips.new(type='KEYFRAME')
# New in this commit:
channelbag = strip.channelbags.new(slot)
strip.channelbags.remove(channelbag)
```
Pull Request: https://projects.blender.org/blender/blender/pulls/124793
7360ce4bcc