fix: Add support for showStudyList configuration setting (#3009)

I followed suit with how it was implemented in the v2 branch, on the 404
page I just hit the link back to the study list if we're not configured
to display it. See PR #2131

extensions/default/src/ViewerLayout/index.tsx

@@ -202,6 +202,7 @@ function ViewerLayout({
     <div>
       <Header
         menuOptions={menuOptions}
+        isReturnEnabled={!!appConfig.showStudyList}
         onClickReturnButton={onClickReturnButton}
         WhiteLabeling={appConfig.whiteLabeling}
       >