Added affinity spec

[josecastillolema]

Changes introduced with this PR

Added pod affinity/antiaffinity spec.

A workflow.yaml example with pod affinity:

...
  pcp:
    plugin: quay.io/dustinblack/arcaflow-plugin-pcp-test:latest
    step: start-pcp
    input:
      pmlogger_interval: !expr $.input.pmlogger_interval
      run_duration: !expr $.input.uperf_server_timeout_seconds
    deploy:
      type: kubernetes
      connection: !expr $.steps.kubeconfig.outputs.success.connection
      pod:
        metadata:
          namespace: default
          labels:
            arcaflow: pcp
        spec:
          pluginContainer:
            imagePullPolicy: IfNotPresent
          affinity:
            podAffinity:
              requiredDuringSchedulingIgnoredDuringExecution:
              - labelSelector:
                  matchExpressions:
                  - key: arcaflow
                    operator: In
                    values:
                    - uperf-client
                topologyKey: node-role.kubernetes.io/worker

A workflow.yaml example with pod antiaffinity:

...
  pcp:
    plugin: quay.io/dustinblack/arcaflow-plugin-pcp-test:latest
    step: start-pcp
    input:
      pmlogger_interval: !expr $.input.pmlogger_interval
      run_duration: !expr $.input.uperf_server_timeout_seconds
    deploy:
      type: kubernetes
      connection: !expr $.steps.kubeconfig.outputs.success.connection
      pod:
        metadata:
          namespace: default
          labels:
            arcaflow: pcp
        spec:
          pluginContainer:
            imagePullPolicy: IfNotPresent
          affinity:
            podAntiAffinity:
              requiredDuringSchedulingIgnoredDuringExecution:
              - labelSelector:
                  matchExpressions:
                  - key: arcaflow
                    operator: In
                    values:
                    - uperf-client
                topologyKey: node-role.kubernetes.io/worker

[jaredoconnell]

Looks good to me. Janos may be able to provide more valuable feedback.

[ghost]

Very nice work!