Fixes: #8758

Description

• add support templating in diagnose command when using --yaml-only
  • add skaffold:template tag to label templated fields, so we can use go template engine to render the specified fields, supported fields are the same as other commands see templated fields ,
  • the feature is guarded by a flag enable-templating in diagnose command, as this feature is a breaking change for users are keeping template place holder when using diagnose command.
  • The implementation doesn't have special handling for templated fields for ko builder as other command which replace {{.ENV with {{, that was for ko-skaffold templates compatibilities , but we've documented that for more than one year https://skaffold.dev/docs/builders/builder-types/ko/#build-flags .ENV is not needed, so treating it as normal templated fields should be fine.
  • The implementation will error out if key is missing when rendering templates.

Schema change

• schema: v4beta11 #9401

Follow-up Work

• the skaffold:template may be used for generating docs to show which fields are templated fields, we may add an issue if the approach in this pr is the way we want to implement the feature .

Alternative Solution

• unmarshal the whole config and then render with go template.
  • Pros:
    • easy to implement
  • Cons:
    • The behavior is not consistent with other commands and the whole skaffold.yaml might be taken as a template file, misuse can lead to unexpected result when skaffold marshal skaffold.yaml -> Skaffold.Configuration struct