mm/damon/core: add DAMOS quota gaol metric for per-memcg per-numa free memory

mm/damon/core: add DAMOS quota gaol metric for per-memcg per-numa free memory

Add a variant of DAMOS_QUOTA_NODE_MEMCG_USED_BP, for the free memory
portion.  The value of the metric is implemented as the entire memory of
the given NUMA node subtracted by the given cgroup's usage.  So from a
perspective, "unused" could be a better term than "free".  But arguably it
is not very clear what is better, so use the term "free".

Link: https://lkml.kernel.org/r/20251017212706.183502-7-sj@kernel.org
Signed-off-by: SeongJae Park <sj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>