feat(init): add validation when initializing VitePress configuration

[0xlau]

close #3641

If the configuration directory of VitePress is outside the project root directory, the project will not run correctly, so add this validation logic to ensure that the path entered by the user is within the root directory.

[0xlau]

@brc-dd 😂 I forgot to checkout the new branch to submit this pr. Do I need to close this pr and resubmit a new one with the new branch instead of 0xlau/main branch.

[brc-dd]

Nah it's fine. Don't close it.