mgr/dashboard: "Please expand your cluster first" shouldn't be shown if cluster is...

mgr/dashboard: "Please expand your cluster first" shouldn't be shown if cluster is already meaningfully running

This PR will assume that a cluster is already up and fully running. If this should not be the expected behaviour, deployment tools have to set 'INSTALLED' explicitly. Without this assumption it might happen that upgraded and fully running clusters, e.g. Octopus -> Pacific, will show the 'Expand Cluster' on first log in.

cephadm will take care that the bootstrap phase will write the necessary key to show the 'Expand cluster' page.

Fixes: https://tracker.ceph.com/issues/54215
Signed-off-by: Volker Theile <vtheile@suse.com>
(cherry picked from commit 48fff60b63785ec07f71d3e59394b0c08357247c)