refactor: show the add snippets button on the centre of the panel

Author: devvaannsh

src/styles/Extn-CustomSnippets.less

@@ -91,6 +91,10 @@
     margin-right: 4px;
 }
 
+#custom-snippets-list {
+    height: 100%;
+}
+
 #custom-snippets-list.hidden {
     display: none;
 }