feat(search): allow complete section customization

This allows configuring the searchable sections and which sections show the search box. In addition the javascript is only included on pages where the search box is visible.

config/_default/params.toml

@@ -83,6 +83,8 @@ lastMod = false
   clipBoard = true
   instantPage = true
   flexSearch = true
+  searchSectionsShow = []
+  searchSectionsIndex = []
   darkMode = true
   bootStrapJs = true
   breadCrumb = false