layouts: add toc_max and toc_min (#22159)

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## Description

Fix toc_min and toc_max for right nav as defined in
https://docs.docker.com/contribute/file-conventions/#front-matter

Comparison with existing `toc_max: 2`:
https://docs.docker.com/desktop/release-notes/

https://deploy-preview-22159--docsdocker.netlify.app/desktop/release-notes/

## Related issues or tickets

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## Reviews

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- [ ] Editorial review

Signed-off-by: Craig <[email protected]>

Author: craig-osterhout

layouts/partials/pagemeta.html

@@ -20,8 +20,8 @@
 {{- end }}
 
 {{- define "walkHeadingFragments" }}
-  {{- $min := 2 }}
-  {{- $max := 3 }}
+  {{- $min := default 2 page.Params.toc_min }}
+  {{- $max := default 3 page.Params.toc_max }}
   <ul class="pl-2">
     {{- range . }}
       {{- if and (ge .Level $min) (le .Level $max) }}