Allow setting mode via environment variable

[rschamp]

Description

I am used to being able to configure my builds in CI via environment variables. E.g., if I have npm run build I would like to be able to use that same command, but have it behave differently based on the environment. Currently I can somewhat affect my build via NODE_ENV=production for a production build and NODE_ENV=development for a staging build. I would like to have the same control for the mode.

Suggested solution

Similarly to NODE_ENV we could have the VITE_MODE or MODE environment variable change the mode.

Alternative

In order to change import.meta.env.MODE, I need a separate command npm run build:staging, or I need to adjust the command I run like npm run build -- --mode staging. These workarounds make my CI config more complex than it could be.

Additional context

No response

Validations

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

[sapphi-red]

If you can put "build": "vite --mode ${VITE_MODE:-production}" (for bash), then I think you can run npm run build/MODE=staging npm run build.