Add existing capabilities of the Bosch BMI270 driver to the Zephyr BMI270 driver (activity change, writst gestures, context)

[ljunquera]

Is your enhancement proposal related to a problem? Please describe.
The Zephyr driver for the Bosch BMI270 Accelerometer/Gyroscope does not support the following capabilities:

1. activity change recognition (still, walking, running)
2. wrist gestures (push arm down, pivot up, wrist shake jiggle, flick in, flick out, wrist wear wake up)
3. context (step counter and step detector, activity change recognition, still, walking, running)

Describe the solution you'd like
I would like to have these features, which are shown in the Bosch BMI270 driver, added to Zephyr.

Describe alternatives you've considered
I've considered writing private drivers, like ZSWatch has done, but it is beyond my expertise and I think it would benefit the community for the capabilities to be in Zephyr.

Additional context
Ideally there would be a way to extend the accelerometer patterns so we could add our own domain specific ones within our projects as well.

[ljunquera]

Is there some way I can help to move this forward?