support gtsam 4.3 header migration

[v4hn]

They recently split this class out in another header in their 4.3 development branch.

[matlabbe]

LGTM! thank you

[matlabbe]

Looks like kilted and rolling are using a 4.3 version older than this change added 2 weeks ago: https://github.com/borglab/gtsam/commits/develop/gtsam/nonlinear/NoiseModelFactorN.h

They just released 3 weeks ago a new version for ros2: https://github.com/borglab/gtsam/issues/2278

[v4hn]

Wonderful. I guess no choice but to wait for ros2 to pull in new versions once things settled down there, because the different development states share the version number. I packaged it for ROS-O in one of the builders last week and found this breaking change. I guess there is no harm in having it lie around depending on your preferences for the master branch.