feat: Provide values of withItems maps as JSON in {{item}}. Fixes #1905

[markterm]

Checklist:

• Either (a) I've created an enhancement proposal and discussed it with the community, (b) this is a bug fix, or (c) this does not need to be in the release notes.
• The title of the PR is (a) conventional, (b) states what changed, and (c) suffixes the related issues number. E.g. "fix(controller): Updates such and such. Fixes #1234". Why? for the release notes.
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• I've signed the CLA and required builds are green.

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (master@59a1906). Click here to learn what that means.
The diff coverage is 50%.

@@            Coverage Diff            @@
##             master    #1906   +/-   ##
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  Coverage          ?   11.17%           
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  Files             ?       35           
  Lines             ?    23541           
  Branches          ?        0           
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  Hits              ?     2630           
  Misses            ?    20573           
  Partials          ?      338

Impacted Files	Coverage Δ
workflow/controller/operator.go	56.27% <50%> (ø)

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[simster7]

LGTM

[sachsbl]

This broke my workflow. Previously there was an extra layer of json deserialization applied to the items in the list, as compared to current.

[simster7]

@sachsbl @salanki Can you guys provide sample workflows, if possible

[sachsbl]

apiVersion: argoproj.io/v1alpha1
kind: WorkflowTemplate
metadata:
  name: workflow-template
spec:
  arguments:
    parameters:
    - name: event-payload
      value: ""
  ttlSecondsAfterFinished: 300
  serviceAccountName: workflow
  entrypoint: workflow-template
  parallelism: 4
  templates:
  - name: workflow-template
    steps:
    - - name: job-creator
        template: job-creator
    - - name: run-job
        template: run-job
        arguments:
          parameters:
          - name: job
            value: "{{item}}"
        withParam: "{{steps.job-creator.outputs.parameters.jobs-list}}"
  - name: job-creator
    podSpecPatch: |
      containers:
        - name: main
          resources:
            requests:
              cpu: 1
              memory: 14336Mi
    container:
      image: workflow
      imagePullPolicy: Always
      command: [python3, "job_creator.py"]
    outputs:
      parameters:
      - name: jobs-list
        valueFrom:
          path: /tmp/jobs_list.json
  - name: run-job
    podSpecPatch: |
      containers:
        - name: main
          resources:
            requests:
              cpu: 2
              memory: 4048Mi
    inputs:
      parameters:
      - name: job
    container:
      image: workflow
      imagePullPolicy: Always
      command: [python3, "process_job.py"]
      args: ["{{inputs.parameters.job}}"]
      volumeMounts:
        - name: nfs-volume
          mountPath: /efs/

[sachsbl]

that workflow still works. However, the value of "{{item}}" passed to the job now has one layer less of json encoding. Honestly this felt like a bug before, and the current behavior makes more sense. It did break though :-)

[salanki]

Please see: #2248