mgr/dashboard: Show warning when replicated size is 1

mgr/dashboard: Show warning when replicated size is 1

Issues a warning when creating a replicated pool and the replicated size
is 1. It won't stop the user from creating the pool, but will give the
user a hint that no replication will be created.

Fixes: https://tracker.ceph.com/issues/42404
Signed-off-by: Sebastian Krah <skrah@suse.com>
(cherry picked from commit af1a7dbfe2b0e2e40650d64d4c3247f4961743c2)

 Conflicts:
	src/pybind/mgr/dashboard/frontend/src/styles/defaults/_bootstrap-defaults.scss
- The file does not exist in octopus, moving a slightly changed version of the diff
  to src/pybind/mgr/dashboard/frontend/src/styles.scss instead