support live diff preview at the level of model abstraction

## Feature

provide live diff preview, so that users will see what changes will be made before actually applying. And the preview should be displayed at the level of model abstraction to avoid the cognitive burden to be aware of infra-oriented details.

## Design

The live diff preview can be triggered by 2 entries:

- Command Palette -> select `Kusion: Preview Live Diff and Apply`
- Right-click on a stack -> click `Preview Live Diff and Apply`

users can:
- see side-to-side diff view with different values highlighted(green for added, red for deleted)
- select or fill in the dynamic parameters for local configurations to digest
- sync runtime configurations to local files by clicking the sync button on the diff lines
- check the diffs, component by component
- navigate through diff blocks up and down with current diff blocks highlighted


Start from the VS Code Command Palette action and the stack context-menu action named in the issue. Review how those two entries can lead to a model-level live diff, then use the listed side-by-side highlighting, dynamic parameters, sync controls, component navigation, and apply flow as the completion criteria.

Written by the indexing model from the issue text.