refactor: centralize page filtering logic, and allow sort by lastmod (#1250)

* refactor: migrate page visibility control from `Params.hidden` to the new `build.list` parameter.

* refactor: centralize page filtering logic into a new `helper/pages.html` partial

* feat: introduce `SortBy` parameter to enable sorting pages by last modified date

* refactor: extract page sorting logic into a new `pages-sort.html` partial

layouts/archives.html

@@ -15,7 +15,7 @@
         {{ end }}
     </header>
 
-    {{ $pages := where .Site.RegularPages "Type" "in" .Site.Params.mainSections }}
+    {{ $pages := partial "helper/pages.html" .Site.Home }}
 
     {{ range $pages.GroupByDate "2006" }}
     {{ $id := lower (replace .Key " " "-") }}