fix: Apply workflow level PodSpecPatch in agent pod. Fixes #12387

[jswxstw]

Fixes #12387

Motivation

We want to schedule the agent pod directly to the virtual node, so we set a workflow-level podSpecPatch nodeName: virtual-node.
However, podSpecPatch was not applied to the agent pod.

Modifications

I apply workflow-level podSpecPatch to the agent pod like the workflowpod does.

Verification

workflow spec demo

apiVersion: argoproj.io/v1alpha1
kind: Workflow
metadata:
  generateName: http-template-
  labels:
    workflows.argoproj.io/test: "true"
  annotations:
    workflows.argoproj.io/description: |
      Http template will demostrate http template functionality
    workflows.argoproj.io/version: '>= 3.2.0'
spec:
  podSpecPatch: |
    nodeName: virtual-node
  entrypoint: main
  templates:
    - name: main
      steps:
        - - name: good
            template: http
            arguments:
              parameters: [{name: url, value: "https://raw.githubusercontent.com/argoproj/argo-workflows/4e450e250168e6b4d51a126b784e90b11a0162bc/pkg/apis/workflow/v1alpha1/generated.swagger.json"}]
  
    - name: http
      inputs:
        parameters:
          - name: url
      http:
       # url: http://dummy.restapiexample.com/api/v1/employees
       url: "{{inputs.parameters.url}}"

[terrytangyuan]

Thanks!