Throw error on build when invalid features are declared via env var

[elboletaire]

This is already being done for login types, although it's a bit precarious, since we're re-declaring a key that is already declared somewhere else.

All this has to be done in vite/features.ts and, since it's outside of the src directory, this can cause import issues for some parts.. so maybe the keys of the things to be declared should be outside, and then re-used both in features and in the code.

If this cannot be done, at least re-declare whatever is necessary in order to get a sort of features validation when building (and when running the dev server too, ofc).

Example of the current implementations for logins can be found here: https://github.com/vocdoni/ui-scaffold/blob/develop/vite/features.ts#L27-L32