Bug 1817600 - Show NordVPN partnership as text link and image. r=frg

An image link is blocked as an advert by ABP and uBLock.

lib/sidebar.tmpl

@@ -68,8 +68,9 @@
    END;
 
    IF template.name == "index.en.html";
-     "<span style=\"font-size: x-small\">Sponsored by:</span><br>\n";
-     "<a href=\"https://go.nordvpn.net/aff_c?offer_id=15&aff_id=81347&url_id=902\">
-         <img src=\"/images/nordvpn-banner.png\" width=\"240\" height=\"240\"></a>";
+     "<span style=\"font-size: x-small\">\n";
+     "<a href=\"https://go.nordvpn.net/aff_c?offer_id=15&aff_id=81347&url_id=902\" target=\"_blank\">"
+     "\"Partnered with NordVPN\"</a></span><br>\n";
+     "<img src=\"/images/nordvpn-banner.png\" width=\"240\" height=\"240\">";
    END;
 %]