Add explicit type for "data-testid"

Author: kraenhansen

packages/lib/src/LgIdProps/index.ts

@@ -10,4 +10,9 @@ export interface LgIdProps {
    * LG test id passed to the component wrapper.
    */
   ['data-lgid']?: LgIdString;
+
+  /**
+   * An additional test id passed to the component wrapper, meant for use by consumers of the library.
+   */
+  ['data-testid']?: string;
 }