unify plan templates

[suzuki-shunsuke]

• plan:

  tfcmt/pkg/config/config.go

  Lines 52 to 54 in a053b0a

  	// Plan is a terraform plan config
  	type Plan struct {
  	Template string

• when_destroy:

  tfcmt/pkg/config/config.go

  Lines 69 to 72 in a053b0a

  	// WhenDestroy is a configuration to notify the plan result contains destroy operation
  	type WhenDestroy struct {
  	Label string
  	Template string