libbpf-tools: add CO-RE 'pidpersec'

[myhro]

This is a CO-RE port of the Brendan Gregg's pidpersec BCC Python tool.

It's my second attempt in porting a BCC tool to CO-RE. I'm starting from the smaller ones, but the intention is to eventually get to the larger ones.

[yonghong-song]

Thanks for contribution. But bcc tools are used for production debugging and observations. You need to provide real use cases for the tool to be merged.

[myhro]

Thanks for the feedback, @yonghong-song. This PR is not a completely new addition, but a C/libbpf port of the existing pidpersec.py tool, which is documented in the companion example.

My understanding is that if a tool is already part of the repository, it's considered useful for production debugging/observations. Maybe this case is different, considering it was added ~9 years ago, and it was just a showcase of BPF functionality back then?