Set canonical link for 4.0 pages to devel

This hopefully helps with removing duplicate hits in Algolia search

Author: Simran-B

site/themes/arangodb-docs-theme/layouts/partials/meta.html

@@ -37,13 +37,12 @@
       {{- if gt $i 2 }}{{ $s = $s | append $e }}{{ end }}
     {{- end }}
     <link rel="canonical" href="{{ delimit $s "/" }}">
+  {{- else if and (eq (.Page.Store.Get "alias") "devel") (not (hasPrefix .RelPermalink "/arangodb/devel/")) }}
+    {{- $splitLink := split .RelPermalink "/" }}
+    {{- $s := slice "/arangodb" "devel" }}
+    {{- range $i, $e := $splitLink }}
+      {{- if gt $i 2 }}{{ $s = $s | append $e }}{{ end }}
+    {{- end }}
+    <link rel="canonical" href="{{ delimit $s "/" }}">
   {{- end }}
-  {{- /* TODO: Set all available versions on non-versioned pages?
-  {{- $shortVersions := slice }}
-  {{- $versions := index site.Data.versions "/arangodb/" }}
-  {{- range $version := $versions }}
-    {{- $shortVersions = $shortVersions | append (cond (eq $version.name $version.alias) $version.name $version.alias) }}
-  {{- end }}
-  <meta name="docsearch:version" content="{{ delimit $shortVersions "," }}">
-  */}}
 {{- end }}