unable to build grid_map on ros2 humble

[Claudio-Chies]

its basically two problems at the same time:
first colcon build --symlink-install --packages-up-to pcl_ros throws me Package 'pcl_ros' specified with --packages-up-to was not found (same issue as in old Issue)

i was able to fix this problem with two things:
take the fix from the issue above and change the branch of perception_pcl from foxy-devel to ros2 (proposed PR: #407)
and then clone the humble branch instead of the ros 2 branch in the readme (Updated Readme PR: #408)