feat: add server name and version to all responses

This is inline with other Subsonic compatible servers, like funkwhale, madsonic, ampache...

consts/version.go

@@ -0,0 +1,20 @@
+package consts
+
+import "fmt"
+
+var (
+	// This will be set in build time. If not, version will be set to "dev"
+	gitTag string
+	gitSha string
+)
+
+// Formats:
+// dev
+// v0.2.0 (5b84188)
+// master (9ed35cb)
+func Version() string {
+	if gitSha == "" {
+		return "dev"
+	}
+	return fmt.Sprintf("%s (%s)", gitTag, gitSha)
+}