Docs/ABI/damon: update for DAMOS apply intervals

Update DAMON ABI document for the newly added DAMON sysfs file for DAMOS
apply intervals (apply_interval_us file).

Link: https://lkml.kernel.org/r/20230916020945.47296-10-sj@kernel.org


Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>