use config.base also in production

[FynniX]

Description

Instead of forcing a base of './' in production it now allows the user to decide via config.
Fixes #466

Additional context

This is needed for example for prerendering in preact where each route has its own html file

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What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Other

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[alex8088]

base option should not be set in production. More details: https://vitejs.dev/config/shared-options.html#base. In production, we use file protocol to load page.