Make prometheus always use VERSION when running upgrade_command, similar to install_command.

We cannot use `version` as there are instances which may have
incompatible values, eg. 2.0.0.

Technially this method is not a way to upgrade the helm chart to a later
version - it was introduced to allow config maps to be updated. We are
yet to address changing helm chart versions

ee/app/models/ee/clusters/applications/prometheus.rb

@@ -7,7 +7,7 @@ module EE
         prepended do
           state_machine :status do
             after_transition any => :updating do |application|
-              application.update(last_update_started_at: Time.now)
+              application.update(last_update_started_at: Time.now, version: application.class.const_get(:VERSION))
             end
           end
         end
@@ -34,11 +34,12 @@ module EE
           ::Gitlab::Kubernetes::Helm::GetCommand.new(name)
         end
 
+        # TODO allow users to chose which version to upgrade to.
         def upgrade_command(values)
           ::Gitlab::Kubernetes::Helm::UpgradeCommand.new(
             name,
+            version: self.class.const_get(:VERSION),
             chart: chart,
-            version: version,
             values: values
           )
         end

ee/spec/models/ee/clusters/applications/prometheus_spec.rb

@@ -12,6 +12,16 @@ describe Clusters::Applications::Prometheus do
         expect { subject.make_updating }.to change { subject.reload.last_update_started_at }.to be_within(1.second).of(Time.now)
       end
     end
+
+    context 'application install previously errored with older version' do
+      subject { create(:clusters_applications_prometheus, :installed, cluster: cluster, version: '6.7.2') }
+
+      it 'updates the application version' do
+        subject.make_updating
+
+        expect(subject.reload.version).to eq('6.7.3')
+      end
+    end
   end
 
   describe '#ready' do
@@ -118,6 +128,7 @@ describe Clusters::Applications::Prometheus do
 
       expect(command.name).to eq('prometheus')
       expect(command.chart).to eq('stable/prometheus')
+      expect(command.version).to eq('6.7.3')
       expect(command.values).to eq(values)
     end
   end