feat: embed threshold and index val of navbar into html/inline js (#241)

* feat: refactor image retrieval logic and improve variable initialization

- Add a new file `layouts/partials/function/getImageSlice.html`
- Initialize variables `$context`, `$Path`, and `$params`
- Set `$Path` based on the result of the `partial/function/currentMenuItem.html` partial
- Retrieve the page `$gallery` based on `$Path`
- Return all resources of type `image` from `$gallery`

* refactor: adapt getImageSlice function to `single.json`

* feat: refactor navigation UI components to use static go template

* feat: update navigation functionality and threshold rendering

layouts/partials/function/getImageSlice.html

@@ -0,0 +1,10 @@
+{{- $context := . -}}
+{{- $Path := "" -}}
+{{- $params := .Page.Params | merge .Site.Params.Page -}}
+
+{{- with partial "function/currentMenuItem.html" . -}}
+  {{- $Path = .Identifier -}}
+{{- end -}}
+
+{{- $gallery := site.GetPage $Path -}}
+{{- return $gallery.Resources.ByType "image" -}}