[Glitch] Add graphs and retention metrics to admin dashboard (#16829)

Port 07341e7aa6 to glitch-soc

Signed-off-by: Claire <claire.github-309c@sitedethib.com>

app/javascript/flavours/glitch/components/skeleton.js

@@ -0,0 +1,11 @@
+import React from 'react';
+import PropTypes from 'prop-types';
+
+const Skeleton = ({ width, height }) => <span className='skeleton' style={{ width, height }}>&zwnj;</span>;
+
+Skeleton.propTypes = {
+  width: PropTypes.number,
+  height: PropTypes.number,
+};
+
+export default Skeleton;