Add "Data updated" date to byline

This seems like important information that shouldn't only be buried at
the bottom of the page.

Keep the existing text at the bottom for users who are used to finding
it there.

Suggested by @joverlee521.

src/components/info/byline.js

@@ -22,6 +22,7 @@ class Byline extends React.Component {
         {renderAvatar(t, this.props.metadata)}
         {renderBuildInfo(t, this.props.metadata)}
         {renderMaintainers(t, this.props.metadata)}
+        {renderDataUpdated(t, this.props.metadata)}
         {renderDataProvenance(t, this.props.metadata)}
       </>
     );
@@ -101,6 +102,20 @@ function renderMaintainers(t, metadata) {
   return null;
 }
 
+/**
+ * Returns a React component detailing the date the data was last updated.
+ * Renders a <span> containing "Data updated X", where X derives from `metadata.updated`
+ */
+function renderDataUpdated(t, metadata) {
+  if (metadata.updated) {
+    return (
+      <span>
+        {`${t("Data updated")} ${metadata.updated}. `}
+      </span>
+    );
+  }
+  return null;
+}
 
 /**
  * Returns a React component detailing the data provenance of the build (pipeline).