PositionDevice tracker should specify frame

[ChristopherRabotin]

Bug report

Describe the bug

The PositionDevice does not seem to specify a frame so it returns the noisy position vector in whichever the frame the trajectory is built in. This is not correct since a GNSS receiver would report data in the WSG84 frame for example.

Further, the position device is not currently exported to Python, but it should be.

To Reproduce

Steps to reproduce the behavior:

1. Provide a trajectory in EME2000
2. Simulate a GNSS tracking arc
3. Kaboom, the position data is in EME2000 instead of ITRF93/WGS84.

Additional context

Also add an orbit determination example that ingests some tracking data and runs the OD filter with it.

[google-labs-jules]

Jules is on it. When finished, you will see another comment and be able to review a PR.

[google-labs-jules]

Ready for a review! A PR has been created.