Support multiple modes

[SpiderUnderUrBed]

I don't think vite has this currently, but it would be very useful if with vite you could specify more than one mode in build flags, you can combine modes into one, and if you have individual actions you need each mode setting to do (which should be the use case for this), you could split it and handle it separately, but it would be cleaner if modes were some sort of overload or there was some way to handle multiple modes.