Create a group exp hex example for side-by-side comparison with existing hex

[Affie]

IIF basically has this already, we just need to create the factor in RoME and decide on a name.
Maybe LiePose2Pose2

[Affie]

See https://github.com/JuliaRobotics/RoME.jl/pull/799/changes#diff-c78e641437af91d02cc9238668f8a40b421899812e5e954a44f51dccd8834651 for a test with the 2 options.

We still need better factor names.