Process the project descriptor

[EricHripko]

Overview

Project description (aka project.toml) is defined here. If present, we should utilise it appropriately:

• project.id can be used to scope the cache
• project.build can be used to control the build context (similar to dockerignore)
• build.env can be injected as build environment variables

As well suggested by @jromero, config package could be responsible for processing this and translating it into BuildKit settings.

[EricHripko]

A separate point of research would be what should happen with build.buildpacks. IIUC, frontend will need to pull any remote buildpacks and inject them into the build environment.