Build: vary cached footer on section

Create a new cached footer for each section set in baseof.html.
This makes sure that pagefind/pagefind-ui.js is included if the
section is "search".

Author: dotnetCarpenter

layouts/_default/baseof.html

@@ -165,7 +165,7 @@ <h1 data-pagefind-meta="title">About{{ if (isset .Params "subtitle") }} - {{ .Pa
           {{ end }}
         </div>
       </div>
-      {{ partialCached "footer.html" . }}
+      {{ partialCached "footer.html" . .Params "section" }}
     </div>
   {{ end }}