Set openapi schema type to file where possible

Jellyfin.Api/Attributes/ProducesFileAttribute.cs

@@ -0,0 +1,28 @@
+using System;
+
+namespace Jellyfin.Api.Attributes
+{
+    /// <summary>
+    /// Internal produces image attribute.
+    /// </summary>
+    [AttributeUsage(AttributeTargets.Method)]
+    public class ProducesFileAttribute : Attribute
+    {
+        private readonly string[] _contentTypes;
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="ProducesFileAttribute"/> class.
+        /// </summary>
+        /// <param name="contentTypes">Content types this endpoint produces.</param>
+        public ProducesFileAttribute(params string[] contentTypes)
+        {
+            _contentTypes = contentTypes;
+        }
+
+        /// <summary>
+        /// Gets the configured content types.
+        /// </summary>
+        /// <returns>the configured content types.</returns>
+        public string[] GetContentTypes() => _contentTypes;
+    }
+}