Rename serve command to preview to align with Vite

[sapphi-red]

Is your feature request related to a problem? Please describe.

Vite uses preview instead of serve. Vitepress uses serve.
I think it's more intuitive to use preview because that will align with Vite.

Describe the solution you'd like

Rename vitepress serve to vitepress preview.

Describe alternatives you've considered

• Add an alias so that vitepress preview works as vitepress serve
• Don't do this.

Additional context

No response

Validations

• Follow our Code of Conduct
• Read the docs.
• Read the Contributing Guidelines.
• Check that there isn't already an issue that asks for the same feature to avoid creating a duplicate.

[sapphi-red]

Thanks!