[BUG] Warning message printed in stdout

[adrienaury]

These kind of warning message are annoying, it breaks lino|pimo pipelines.

LINO/internal/app/urlbuilder/urlbuilder.go

Line 141 in 34eb10a

fmt.Fprintf(out, "warn: missing environment variable %s", dc.User.ValueFromEnv)

It should be a log in stderr with warning level