Set openapi schema type to file where possible

Jellyfin.Api/Attributes/ProducesAudioFileAttribute.cs

@@ -0,0 +1,18 @@
+namespace Jellyfin.Api.Attributes
+{
+    /// <summary>
+    /// Produces file attribute of "image/*".
+    /// </summary>
+    public class ProducesAudioFileAttribute : ProducesFileAttribute
+    {
+        private const string ContentType = "audio/*";
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="ProducesAudioFileAttribute"/> class.
+        /// </summary>
+        public ProducesAudioFileAttribute()
+            : base(ContentType)
+        {
+        }
+    }
+}