[Proposal] supporting to config sealer app to enrich the clusterfile's capabilities

[kakaZhou719]

Issue Description

Type: feature request

Describe what feature you want

currently ,we can support launching the corresponding app through ClusterSpec.APPNames,
Or directly use ClusterSpec.CMD to overwrite the app launch cmds.

however, for different types of apps, we have different startup commands and launch files， could we precisely support the configuration of the app at run stage?

so i proposal that we could add Application kind as below, for extensibility supporting config the sealer app and enrich the clusterfile's capabilities

1. for app files: We can modify the app file content according to the specified file path, such as overwrite,merge,render.
2. for app launch and delete: We can configure the corresponding launch or delete depending on the type of app, such as helm,kube,shell. At the same time, we can also support the raw launch command line.
3. for cmds and appNames they are mutually exclusive, could be overwrite from clusterspec and cli flags.
   4. for env its a global key pair used to do render(kube),export shell env(shell), set values.yaml(helm).

apiVersion: sealer.io/v2
kind: Application
metadata:
  name: my-apps
spec:
    image: my-app:v1
    cmds: 
      - kubectl apply -f ns.yaml
    appNames: 
      - app1
      - app2
      - app3
    configs:
    - name: app1
      delete :
         - kubectl delete -f ns.yaml
         - kubectl delete -f nginx.yaml -n namespace
      launch:
        cmds:
          - kubectl apply -f ns.yaml
          - kubectl apply -f nginx.yaml -n namespace
      files:
        - filePath: ns.yaml
          valueType: 'raw(overwrite),args(render),secret,namespace'
          values:
            - key1=value1
            - key2=value2
    - name: app2
      launch:
        cmds:
          - helm install my-nginx bitnami/nginx
        helm:
          chartName: my-nginx
          namespace: sealer
          values:
            - key1=value1
            - key2=value2
      files:
        - filePath: values.yaml
          valueType: raw
          values:
            - key1=value1
            - key2=value2
    - name: app3
      launch:
        cmds:
          - bash nginx.sh
        shell:
          env:
            - key1=value1
            - key2=value2
          filePath:
            - preinstall.sh
            - nginx.sh
      files:
        - filePath: preinstall.sh
          valueType: raw
          values: |
            kubectl create ns sealer            
            

Additional context

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