Add support for BPF tokens (#36134)

Add a new option `PrivateBPF=` to mount a private instance of bpffs.
Add also four configuration options
`BPFDelegate{Commands,Maps,Programs,Attachments}=` which set the
corresponding bpffs mount options in order to create BPF tokens:
https://lwn.net/Articles/947173/

Closes#35108.