selftests/damon: add a test for DAMOS quota

selftests/damon: add a test for DAMOS quota

Add a selftest for verifying the DAMOS quota feature.  The test is very
similar to sysfs_update_schemes_tried_regions_wss_estimation.py.  It
starts an artificial workload of 20 MiB working set, run DAMON to find the
working set size, but with 1 MiB/100 ms size quota.  Then, it collect the
DAMON-found working set size every 100 ms and check if the quota was
always applied as expected.  For the confirmation, the tests shows the
stat-applied region size and the qt_exceeds stat.

Link: https://lkml.kernel.org/r/20240207203134.69976-5-sj@kernel.org
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>