feat: add inlineConfig.envFile option to disable .env files

[egoist]

This feature is primarily for frameworks that use Vite under the hood:

• Frameworks might need to load .env before starting Vite dev server, so they use the loadEnv function provided by Vite.
• Vite loads .env again when it's unnecessary
• Vite restarts when .env changes but this should be left to user in this case

[egoist]

Tests work locally, but somehow it failed on circleci.

[antfu]

Failure is unrelated.