Upgrade GPMP2 to use latest GTSAM

[varunagrawal]

This PR upgrades GPMP2 to follow the new paradigm of GTSAM that foregoes Boost. I have updated the codebase accordingly.

Here are the task items that need to be satisfied to land this PR:

• [x] C++ tests pass.
• [x] CI passes.
• [x] Python wrapper compiles.
• [x] Python examples run.
• [x] Matlab wrapper compiles.
• [x] Matlab examples run.
• [x] @mattking-smith's work continues to operate as before.

[varunagrawal]

CI is failing due to std library issues. Will look at it once I get to a desktop.

[mattking-smith]

Looks good! 😺