TrajectoryFileInfo only declares/allows a PerspectiveCameraSpec

[toloudis]

Use Case

In the viewer code, the cameraDefault field of TrajectoryFileInfo is currently typed as a PerspectiveCameraSpec and since we offer ortho cameras, it makes sense to generalize the cameraDefault field.
See simularium/simularium-viewer#330 possibly related.
cameraDefault: PerspectiveCameraSpec;

Acceptance Criteria

Ensure that users can define ortho cameras in their trajectory files. Assuming they can, then allow it in the viewer (change cameraDefault type to CameraSpec) and verify we can load trajectories with either perspective or ortho default cameras.

[meganrm]

would be nice for the education module