doc/cephfs: add cache pressure information

doc/cephfs: add cache pressure information

Add information to doc/cephfs/cache-configuration.rst about how to deal
with a message that reads "clients failing to respond to cache
pressure". This procedure explains how to slow the growth of the
recall_caps value so that it does not exceed the
mds_recall_warning_threshold.

The information in this commit was developed by Eugen Block. See
https://lists.ceph.io/hyperkitty/list/ceph-users@ceph.io/thread/5ROH5CWKKOEIQMVXOVRT5OO7CWK2HPM3/#J65DFUPP4BY57MICPANXKI7KAXSZ5Z5P
and https://www.spinics.net/lists/ceph-users/msg73188.html.

Fixes: https://tracker.ceph.com/issues/57115
Co-authored-by: Eugen Block <eblock@nde.ag>
Signed-off-by: Zac Dover <zac.dover@proton.me>
(cherry picked from commit bf26274ae4737417193f8c2b56bea20eb2a358aa)