Config values at build time

[raphaeltm]

It could be helpful to have access to config values at build time. Maybe this ties into the interpolation issue.

Edit:
For clarity, I'm thinking of build processes that might need to connect to a database, or CMS, or something to generate static artifacts, for example.

[lionello]

I wonder if this has implications for caching builds. Like, if the build depends on $REDIS, and the values changes, should it invalidate/ignore the cache? I suppose there's no way to find out, so no choice but to build from scratch.