Deal with CMP0167 - FindBoost module has been removed

[ManifoldFR]

In the CMake docs: https://cmake.org/cmake/help/latest/policy/CMP0167.html.

The TLDR is that CMake no longer provides the FindBoost.cmake module (which we vendor ourselves), and just delegates to the Boost libraries' included BoostConfig.cmake - which are provided starting Boost 1.70.
Calls to find_package(Boost) now need to be find_package(Boost CONFIG).

• We could remove the FindBoost.cmake copy we include with jrl-cmakemodules, I think. It contains the old logic for finding Boost, and Boost itself now provides its own find module.
• We need to either set the policy for old-style calls to find_package(Boost) to function, or fix the add_project_dependency calls that find Boost in our downstream projects (of the top of my head: eigenpy, pinocchio).

[ManifoldFR]

I remember you did something on aligator related to this a few weeks back @jorisv ?