qa/suites/rados/singleton/all: init mon-stretch-pool.yaml

qa/suites/rados/singleton/all: init mon-stretch-pool.yaml

Test the following new Ceph CLI commands:

`ceph osd pool stretch set`
`ceph osd pool stretch unset`
`ceph osd pool stretch show`

`qa/workunits/mon/mon-stretch-pool.sh`

will create the stretch cluster
while performing input validation for the CLI
Commands mentioned above.

`qa/tasks/stretch_cluster.py`

is in charge of
setting a pool to stretch cluster
and checks whether it prevents PGs
from the going active when there is not
enough buckets available in the acting
set of PGs to go active.

Also, test different MON fail over scenarios
after setting pool as stretch

`qa/suites/rados/singleton/all/mon-stretch-pool.yaml`

brings the scripts together.

Fixes: https://tracker.ceph.com/issues/64802
Signed-off-by: Kamoltat <ksirivad@redhat.com>
(cherry picked from commit 4ca1320727d1f7dca2ddfe7ad1a0b76f95b80ab0)

Conflicts:
	- qa/tasks/ceph_test_case.py (trivial fix)