fix: Allow script and container image to be set in templateDefault. Fixes #9633

[RoryDoherty]

Made changes to validation to check if the script/container Image has been set in templateDefaults

Testing
Added unit tests to verify these situations

Also created the following via the locally deployed UI and then submitted both via the UI and they were successful:

apiVersion: argoproj.io/v1alpha1
kind: WorkflowTemplate
metadata:
  generateName: demo-
spec:
  entrypoint: demo
  templateDefaults:
    script:
      image: alpine:latest
      command: [sh]
      workingDir: "/src"
  templates:
    - name: demo
      script:
        source: |
          pwd

and a cron workflow

apiVersion: argoproj.io/v1alpha1
kind: CronWorkflow
metadata:
  generateName: demo-cron
spec:
  schedule: "00 4 * * 2"
  timezone: "UTC"
  workflowMetadata:
    generateName: demo-cron-test-
  workflowSpec:
    entrypoint: demo
    templateDefaults:
      script:
        image: alpine:latest
        command: [sh]
        workingDir: "/src"
    templates:
      - name: demo
        script:
          source: |
            pwd

Fixes #9633

[terrytangyuan]

Could you also add a test for the functionality, e.g. e2e test?

[RoryDoherty]

Could you also add a test for the functionality, e.g. e2e test?

@terrytangyuan sure no problem, do you have a particular suite or file you would like it added to?

[terrytangyuan]

Possibly here: https://github.com/argoproj/argo-workflows/tree/master/test/e2e/functional