[Artifacts] Prepare for v2.0.0 of @actions/artifact (#1479)

* Prepare for v2.0.0 of @actions/artifact

* Run prettier

* temporary disable unused vars

packages/artifact/src/internal/client.ts

@@ -0,0 +1,44 @@
+import {UploadOptions} from './upload/upload-options'
+import {UploadResponse} from './upload/upload-response'
+import {uploadArtifact} from './upload/upload-artifact'
+
+export interface ArtifactClient {
+  /**
+   * Uploads an artifact
+   *
+   * @param name the name of the artifact, required
+   * @param files a list of absolute or relative paths that denote what files should be uploaded
+   * @param rootDirectory an absolute or relative file path that denotes the root parent directory of the files being uploaded
+   * @param options extra options for customizing the upload behavior
+   * @returns single UploadInfo object
+   */
+  uploadArtifact(
+    name: string,
+    files: string[],
+    rootDirectory: string,
+    options?: UploadOptions
+  ): Promise<UploadResponse>
+
+  // TODO Download functionality
+}
+
+export class Client implements ArtifactClient {
+  /**
+   * Constructs a Client
+   */
+  static create(): Client {
+    return new Client()
+  }
+
+  /**
+   * Uploads an artifact
+   */
+  async uploadArtifact(
+    name: string,
+    files: string[],
+    rootDirectory: string,
+    options?: UploadOptions | undefined
+  ): Promise<UploadResponse> {
+    return uploadArtifact(name, files, rootDirectory, options)
+  }
+}