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/Contracts/Artifact.cs

@@ -0,0 +1,46 @@
+using System.Runtime.Serialization;
+using GitHub.Actions.Pipelines.WebApi.Contracts;
+using Newtonsoft.Json;
+
+namespace GitHub.Actions.Pipelines.WebApi
+{
+    [DataContract]
+    [KnownType(typeof(ActionsStorageArtifact))]
+    [JsonConverter(typeof(ArtifactJsonConverter))]
+    public class Artifact
+    {
+        public Artifact(ArtifactType type)
+        {
+            Type = type;
+        }
+
+        /// <summary>
+        /// The type of the artifact.
+        /// </summary>
+        [DataMember]
+        public ArtifactType Type
+        {
+            get;
+        }
+
+        /// <summary>
+        /// The name of the artifact.
+        /// </summary>
+        [DataMember]
+        public string Name
+        {
+            get;
+            set;
+        }
+
+        /// <summary>
+        /// Self-referential url
+        /// </summary>
+        [DataMember]
+        public string Url
+        {
+            get;
+            set;
+        }
+     }
+}