feat: allow to specify default backend for model (#156)

Signed-off-by: mudler <mudler@c3os.io>

api/config.go

@@ -21,6 +21,7 @@ type Config struct {
 	Threads        int               `yaml:"threads"`
 	Debug          bool              `yaml:"debug"`
 	Roles          map[string]string `yaml:"roles"`
+	Backend        string            `yaml:"backend"`
 	TemplateConfig TemplateConfig    `yaml:"template"`
 }