qa/suites/crimson-rados/singleton: add install task

This should fix the chmod 777 /var/log/ceph failures.

We were missing the install task which resulted in no /var/log/ceph:
```
2025-07-07T08:55:44.586 INFO:teuthology.run_tasks:Running task ceph...
2025-07-07T08:55:44.679 INFO:tasks.ceph:Making ceph log dir writeable by
non-root...
2025-07-07T08:55:44.679 DEBUG:teuthology.orchestra.run.smithi144:> sudo
chmod 777 /var/log/ceph
2025-07-07T08:55:44.711
INFO:teuthology.orchestra.run.smithi144.stderr:chmod: cannot access
'/var/log/ceph': No such file or directory
```

Signed-off-by: Matan Breizman <[email protected]>

Author: Matan-B

qa/suites/crimson-rados/singleton/all/osd-backfill.yaml

@@ -11,6 +11,7 @@ openstack:
       count: 3
       size: 10 # GB
 tasks:
+- install:
 - ceph:
     pre-mgr-commands:
       - sudo ceph config set mgr mgr_pool false --force

qa/suites/crimson-rados/singleton/all/osd-pg-splitting.yaml

@@ -12,6 +12,7 @@ openstack:
       count: 3
       size: 10 # GB
 tasks:
+- install:
 - ceph:
     pre-mgr-commands:
       - sudo ceph config set mgr mgr_pool false --force