Add option to run only once

[MPParsley]

Added option RUNONCE.

It will shutdown the process after running it once.

Useful when running the service as a Kubernetes CronJob:

kind: CronJob
apiVersion: batch/v1
metadata:
  name: ldes-consumer-cronjob
spec:
  schedule: '* * * * *'
  concurrencyPolicy: Forbid
  suspend: false
  jobTemplate:
    spec:
      template:
        spec:
          containers:
            - name: ldes-consumer
              env:
                - name: RUNONCE
                  value: true
                - name: CRON_PATTERN
                  value: * * * * * *
              ports:
                - containerPort: 8080
                  protocol: TCP
              imagePullPolicy: IfNotPresent
              image: redpencilio/ldes-consumer
          restartPolicy: OnFailure
          securityContext: {}
          schedulerName: default-scheduler