helm: lower job-status-consumer prefetch value

- set job-status-consumer RabbitMQ prefetch value to 10;
- this should reduce the risk of getting 406 PRECONDITION error on message ack, and possibly consumer disconnection issue.

addresses reanahub/reana-workflow-controller#436

helm/reana/README.md

@@ -46,7 +46,7 @@ This Helm automatically prefixes all names using the release name to avoid colli
 | `components.reana_workflow_controller.imagePullPolicy`   | REANA-Workflow-Controller image pull policy                                          | IfNotPresent                                    |
 | `components.reana_workflow_controller.environment.REANA_JOB_HOSTPATH_MOUNTS`   | JSON list of optional hostPath mounts, for all user jobs. Each mount object has a key `name` (name of the mount), `hostPath` (path to the directory to be mounted from the Kubernetes nodes) and `mountPath` (path inside the job containers where the `hostPath` will be mounted)            | None                                            |
 | `components.reana_workflow_controller.environment.REANA_RUNTIME_KUBERNETES_KEEP_ALIVE_JOBS_WITH_STATUSES` | Keep alive Kubernetes user runtime jobs depending on status (`finished` and/or `failed`). | None |
-| `components.reana_workflow_controller.environment.REANA_JOB_STATUS_CONSUMER_PREFETCH_COUNT` | Define max number of unacknowledged deliveries that are permitted on `jobs-status` queue consumer. | 200 |
+| `components.reana_workflow_controller.environment.REANA_JOB_STATUS_CONSUMER_PREFETCH_COUNT` | Define max number of unacknowledged deliveries that are permitted on `jobs-status` queue consumer. | 10 |
 | `components.reana_workflow_engine_cwl.image`             | [REANA-Workflow-Engine-CWL image](https://hub.docker.com/r/reanahub/reana-workflow-engine-cwl) to use | `reanahub/reana-workflow-engine-cwl:<chart-release-version>` |
 | `components.reana_workflow_engine_serial.image`          | [REANA-Workflow-Engine-Serial image](https://hub.docker.com/r/reanahub/reana-workflow-engine-serial) to use | `reanahub/reana-workflow-engine-serial:<chart-release-version>` |
 | `components.reana_workflow_engine_yadage.image`          | [REANA-Workflow-Engine-Yadage image](https://hub.docker.com/r/reanahub/reana-workflow-engine-yadage) to use | `reanahub/reana-workflow-engine-yadage:<chart-release-version>` |

helm/reana/values.yaml

@@ -85,7 +85,7 @@ components:
     image: reanahub/reana-workflow-controller:0.9.0-alpha.2
     environment:
       SHARED_VOLUME_PATH: /var/reana
-      REANA_JOB_STATUS_CONSUMER_PREFETCH_COUNT: 200
+      REANA_JOB_STATUS_CONSUMER_PREFETCH_COUNT: 10
   reana_workflow_engine_cwl:
     image: reanahub/reana-workflow-engine-cwl:0.9.0-alpha.2
   reana_workflow_engine_yadage: