Make enum values typed strings (#18)

This also moves validation into the parsing process and refactors a bunch of code related to the config.

Reviewed-on: #18
Co-authored-by: Anna Rose Wiggins <annabunches@gmail.com>
Co-committed-by: Anna Rose Wiggins <annabunches@gmail.com>

internal/configparser/deviceconfig.go

@@ -0,0 +1,31 @@
+package configparser
+
+// These top-level structs use custom unmarshaling to unpack each available sub-type
+type DeviceConfig struct {
+	Type   DeviceType
+	Config interface{}
+}
+
+func (dc *DeviceConfig) UnmarshalYAML(unmarshal func(data interface{}) error) error {
+	metaConfig := &struct {
+		Type DeviceType
+	}{}
+	err := unmarshal(metaConfig)
+	if err != nil {
+		return err
+	}
+	dc.Type = metaConfig.Type
+
+	err = nil
+	switch metaConfig.Type {
+	case DeviceTypePhysical:
+		config := DeviceConfigPhysical{}
+		err = unmarshal(&config)
+		dc.Config = config
+	case DeviceTypeVirtual:
+		config := DeviceConfigVirtual{}
+		err = unmarshal(&config)
+		dc.Config = config
+	}
+	return err
+}