Implement setting default values in plugins

[Warashi]

What would you like to be added:

Implement setting default values in the application config when loading in all plugins.

Why is this needed:

In #6168, we stopped setting default values when loading application config in the SDK. So we need to implement setting default values in plugins.

[t-kikuc]

TODO

Deployment plugins

• [ ] k8s
  • desc:
• [ ] k8s multicluster
  • desc:
• [ ] terraform
  • desc:
• [ ] cloudrun services
  • desc:

Stage plugins

• [ ] wait
  • desc:
• [ ] waitApproval
  • desc:
• [ ] analysis
  • desc:
• [x] scriptRun
  • desc: it already has defaults.Set() https://github.com/pipe-cd/pipecd/blob/45a82f79be938544e374655ff4698d8702b2e2fc/pkg/app/pipedv1/plugin/scriptrun/options.go#L40-L54

community-plugins

• [ ] notify to developers