New: Author folder hint when selecting a root folder while adding a new author

(cherry picked from commit dd09f31abb4dd3f699bcff0a47577075300c70ee)

Fix AuthorFolderAsRootFolderValidator

(cherry picked from commit 0ce81e1ab69d43fde382cc4ae22cd46fe626dea7)

frontend/src/Components/Form/RootFolderSelectInputOption.css

@@ -13,6 +13,15 @@
   }
 }
 
+.value {
+  display: flex;
+}
+
+.authorFolder {
+  flex: 0 0 auto;
+  color: var(--disabledColor);
+}
+
 .freeSpace {
   margin-left: 15px;
   color: var(--darkGray);