[services] Export DatabaseManagers as CMake Project

Summary:
This is part of a larger effort to bring more structure to the C++ codebase https://linear.app/comm/issue/ENG-1310/export-nativecpp-projects-as-cmake-projects

The intent is to be able to reference the dependencies as packages, instead of just as GLOB'ing over certain directories; which is a major anti-pattern in CMake as it create a bunch of footguns such as finding multiple files with main() defined, or picking up unrelated code in generated folders.

Export DatabaseManagers as a CMake Project

Test Plan:

nix develop
cd native/cpp/CommonCpp/DatabaseManagers
rm -rf build && mkdir build && cd build && cmake .. & make -j

Reviewers: max, karol, atul, varun

Reviewed By: atul

Subscribers: abosh, atul, adrian, tomek, ashoat

Differential Revision: https://phab.comm.dev/D4431