[cmake] Removed boost-mp11 from cpm (is part of Boost itself).
boost-mp11 is a regular Boost lib and can therefore directly be used.
- Updated our CPM boost subset tar to include the lib, see https://gitlab.opengeosys.org/ogs/libs/boost-subset/-/merge_requests/1.
- Bumped Boost minimum to 1.73.0
Edited by Lars Bilke