Support downloading/publishing artifacts from Pipelines endpoint (#188)

* Support downloading/publishing artifacts from Pipelines endpoint
* Remove `Path` from everywhere
* Remove unused JobId argument
* PR feedback
* More PR feedback

src/Sdk/PipelinesWebApi/UnknownEnumJsonConverter.cs

@@ -0,0 +1,53 @@
+using System;
+using System.Linq;
+using Newtonsoft.Json;
+using Newtonsoft.Json.Converters;
+
+namespace GitHub.Actions.Pipelines.WebApi
+{
+    public class UnknownEnumJsonConverter : StringEnumConverter
+    {
+        public UnknownEnumJsonConverter()
+        {
+            this.CamelCaseText = true;
+        }
+
+        public override bool CanConvert(Type objectType)
+        {
+            // we require one member to be named "Unknown"
+            return objectType.IsEnum && Enum.GetNames(objectType).Any(name => string.Equals(name, UnknownName, StringComparison.OrdinalIgnoreCase));
+        }
+
+        public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
+        {
+            // Newtonsoft doesn't call CanConvert if you specify the converter using a JsonConverter attribute
+            // they just assume you know what you're doing :)
+            if (!CanConvert(objectType))
+            {
+                // if there's no Unknown value, fall back to the StringEnumConverter behavior
+                return base.ReadJson(reader, objectType, existingValue, serializer);
+            }
+
+            if (reader.TokenType == JsonToken.Integer)
+            {
+                var intValue = Convert.ToInt32(reader.Value);
+                var values = (int[])Enum.GetValues(objectType);
+                if (values.Contains(intValue))
+                {
+                    return Enum.Parse(objectType, intValue.ToString());
+                }
+            }
+
+            if (reader.TokenType == JsonToken.String)
+            {
+                var stringValue = reader.Value.ToString();
+                return UnknownEnum.Parse(objectType, stringValue);
+            }
+
+            // we know there's an Unknown value because CanConvert returned true
+            return Enum.Parse(objectType, UnknownName);
+        }
+
+        private const string UnknownName = "Unknown";
+    }
+}