[New Feature]: Validation only dependency

### Description of the new feature/enhancement

There are cases that submitted package depends on other packages while they *don't* want it to be resolved during `winget install` phase.

Let's say I have a component depends on Java but I want the user to choose JRE/JDK including which provider's, so that the package providers can preserve endusers environment as much as they can while minimizing the installation footprint.

As far as I know, what we can do now is either:
(1) include a small JRE made with jlink, with additional 50-80MB footprint
(2) specify the JRE/JDK as dependency anyway, with additional 300MB footprint
(3) let the validation fail and explain that it is intended, to a moderator to pass the validation, or
(4) explicitly ask enduser to use `--skip-dependencies` option for winget

My proposal is:
(5) specify dependencies only validation for automated package validation and winget do not install them during winget install, but it might be a good idea to print the validation dependency to the user

### Proposed technical implementation details (optional)

It requires:
- new manifest schema
- validation hook

optionally:
- winget prints validation dependency, or
- winget option to `--include-validation-dependencies` or something.

The issue does not name files, tests, or existing entry points. Start by tracing the manifest schema and automated validation flow, then inspect how winget resolves dependencies during install; done would require an agreed schema and validation behavior, with installation behavior and any user-facing output covered by tests.

Written by the indexing model from the issue text.