Add ability to interpolate during build

Now build takes a --values argument, which is a yaml file that can be
used to interpolate the specs that are going to be compiled.

pkg/compiler/interface.go

@@ -56,6 +56,7 @@ type CompilerOptions struct {
 	NoDeps               bool
 	SolverOptions        config.LuetSolverOptions
 	SkipIfMetadataExists bool
+	BuildValuesFile      string
 
 	PackageTargetOnly bool
 }