test(keycloak): Add helm recommendations test

This patch should simply check all resources created by the chart to
contain the recommended Kubernetes labels to be properly identified as
part of the helm chart.

References:
https://kubernetes.io/docs/concepts/overview/working-with-objects/common-labels/

charts/keycloak/tests/helmlabels_test.yaml

+suite: Kubernetes recommendations
+templates:
+  - deployment.yaml
+  - poddisruptionbudget.yaml
+  - networkpolicy.yaml
+  - secret.yaml
+  - service.yaml
+  - serviceaccount.yaml
+  - servicemonitor.yaml
+tests:
+  - it: should have the kubernetes recommended labels
+    set:
+      replicaCount: 2
+      keycloak:
+        database:
+          username: example-db-user
+          password: example-db-password
+          url: example-db-url
+      networkPolicy:
+        create: true
+      metrics:
+        enabled: true
+    release:
+      name: "test-suite"
+    chart:
+      version: 1.2.3
+    asserts:
+      - equal:
+          path: metadata.labels.[app.kubernetes.io/instance]
+          value: "test-suite"
+      - equal:
+          path: metadata.labels.[app.kubernetes.io/managed-by]
+          value: "Helm"
+      - equal:
+          path: metadata.labels.[app.kubernetes.io/name]
+          value: "keycloak"