selftests/bpf: Add uprobe multi pid filter test for clone-ed processes

The idea is to run same test as for test_pid_filter_process, but instead
of standard fork-ed process we create the process with clone(CLONE_VM..)
to make sure the thread leader process filter works properly in this case.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20240905115124.1503998-5-jolsa@kernel.org