Michal Rostecki bf2164c92f feat(aya): Add iterator program type
BPF iterators[0] are a way to dump kernel data into user-space and an
alternative to `/proc` filesystem.

This change adds support for BPF iterators on the user-space side. It
provides a possibility to retrieve the outputs of BPF iterator programs
both from sync and async Rust code.

[0] https://docs.kernel.org/bpf/bpf_iterators.html
..
ext.bpf.c integration-test: avoid reliance on kernel headers
iter.bpf.c feat(aya): Add iterator program type
main.bpf.c integration-test: avoid reliance on kernel headers
multimap-btf.bpf.c integration-test: Add map pinning coverage
reloc.bpf.c aya-obj: Handle lack of match of enum variants correctly
text_64_64_reloc.c integration-test: avoid reliance on kernel headers
variables_reloc.bpf.c test: Reproduce relocation bug