docs: BPF_MAP_TYPE_SOCK[MAP|HASH]

Add documentation for BPF_MAP_TYPE_SOCK[MAP|HASH]
including kernel versions introduced, usage
and examples.

Signed-off-by: Maryam Tahhan <mtahhan@redhat.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Reviewed-by: Bagas Sanjaya <bagasdotme@gmail.com>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Acked-by: David Vernet <void@manifault.com>
Link: https://lore.kernel.org/bpf/20221219095512.26534-1-mtahhan@redhat.com