Add an option to specify container capabilities for the redis container

With some kubernetes clusters and settings, you might need to specify
some capabilities so the container can start. For example, the CHOWN,
SETUID and SETGID capabilties.
Setting the redis_capabilities option will add the capabilities in
the deployment.

roles/installer/templates/deployment.yaml.j2

@@ -74,6 +74,11 @@ spec:
         - image: '{{ redis_image }}:{{ redis_image_version }}'
           imagePullPolicy: '{{ image_pull_policy }}'
           name: redis
+{% if redis_capabilities is defined and redis_capabilities %}
+          securityContext:
+            capabilities:
+              add: {{ redis_capabilities }}
+{% endif %}
           args: ["redis-server", "/etc/redis.conf"]
           volumeMounts:
             - name: {{ ansible_operator_meta.name }}-redis-config