bpf: One more maintainer for libbpf and BPF selftests

I've been working on BPF verifier, BPF selftests and, to some extent,
libbpf, for some time. As suggested by Andrii and Alexei,
I humbly ask to add me to maintainers list:
- As reviewer   for BPF [GENERAL]
- As maintainer for BPF [LIBRARY]
- As maintainer for BPF [SELFTESTS]

This patch adds dedicated entries to MAINTAINERS.

Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/r/20240126032554.9697-1-eddyz87@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>