BPF canonical monitoring agent example

Various projects are adding BPF to their existing monitoring agents. We should have some canonical documentation or examples we can point people to, which use libbcc/libbpf, so they don't reinvent the wheel. Eg, under examples/monitoring.

For C++, the existing examples/cpp/LLCStat.cc looks similar to what I had in mind. I don't know if the Python examples are ok for this use case (someone who is working on Python monitoring software can comment).