When using libraries, cpm could try to download and install them automatically

Libraries declared in the project descriptor could be downloaded and installed automatically by cpm. That could be a solution for a number of problems that arise with the current model. For example, when compiling for raspberrypi4 targets, if the compilation requires for example `boost_filesystem`, then the base image from docker cpmbits won't work, as the library is not installed in the docker image. If `cpm` installed automatically the library, then this problem would be solved as well, besides being a really convenient way of dealing with dependencies.

Start by locating how cpm reads the project descriptor and currently resolves libraries. Investigate the dependency cases mentioned for raspberrypi4 targets, docker cpmbits images, and boost_filesystem. Done should include a defined approach for automatic download and installation, with its dependency behavior and scope documented.

Written by the indexing model from the issue text.