bpf: Add a new kfunc for cgroup1 hierarchy

A new kfunc is added to acquire cgroup1 of a task:

- bpf_task_get_cgroup1
  Acquires the associated cgroup of a task whithin a specific cgroup1
  hierarchy. The cgroup1 hierarchy is identified by its hierarchy ID.

This new kfunc enables the tracing of tasks within a designated
container or cgroup directory in BPF programs.

Suggested-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
Acked-by: Tejun Heo <tj@kernel.org>
Link: https://lore.kernel.org/r/20231111090034.4248-2-laoar.shao@gmail.com


Signed-off-by: Alexei Starovoitov <ast@kernel.org>