feat(subsonic): expose replaygain tags

server/ctrlsubsonic/spec/spec.go

@@ -169,6 +169,13 @@ type TranscodeMeta struct {
 	TranscodedSuffix      string `xml:"transcodedSuffix,attr,omitempty"      json:"transcodedSuffix,omitempty"`
 }
 
+type ReplayGain struct {
+	TrackGain float32 `xml:"trackGain,attr" json:"trackGain"`
+	TrackPeak float32 `xml:"trackPeak,attr" json:"trackPeak"`
+	AlbumGain float32 `xml:"albumGain,attr" json:"albumGain"`
+	AlbumPeak float32 `xml:"albumPeak,attr" json:"albumPeak"`
+}
+
 // https://opensubsonic.netlify.app/docs/responses/child/
 type TrackChild struct {
 	ID      *specid.ID `xml:"id,attr,omitempty"          json:"id,omitempty"`
@@ -211,6 +218,8 @@ type TrackChild struct {
 	UserRating    int        `xml:"userRating,attr,omitempty"      json:"userRating,omitempty"`
 	AverageRating string     `xml:"averageRating,attr,omitempty"   json:"averageRating,omitempty"`
 
+	ReplayGain *ReplayGain `xml:"replayGain" json:"replayGain"`
+
 	TranscodeMeta
 }