Use new 'Image render hook' template from Hugo. (adityatelange#1526)

* Pull render-image template from Hugo
https://github.com/gohugoio/hugo/commits/master/tpl/tplimpl/embedded/templates/_default/_markup/render-image.html

cloned at b893a09aa62c01a62e32b0effdb02e86b51d46d6

* Add loading=lazy attribute

adityatelange@2481a8c

layouts/_default/_markup/render-image.html

@@ -1 +1,22 @@
-<img loading="lazy" src="{{ .Destination | safeURL }}" alt="{{ .Text }}" {{ with .Title}} title="{{ . }}" {{ end }} />
+{{- $u := urls.Parse .Destination -}}
+{{- $src := $u.String -}}
+{{- if not $u.IsAbs -}}
+  {{- $path := strings.TrimPrefix "./" $u.Path }}
+  {{- with or (.PageInner.Resources.Get $path) (resources.Get $path) -}}
+    {{- $src = .RelPermalink -}}
+    {{- with $u.RawQuery -}}
+      {{- $src = printf "%s?%s" $src . -}}
+    {{- end -}}
+    {{- with $u.Fragment -}}
+      {{- $src = printf "%s#%s" $src . -}}
+    {{- end -}}
+  {{- end -}}
+{{- end -}}
+{{- $attributes := merge .Attributes (dict "alt" .Text "src" $src "title" (.Title | transform.HTMLEscape) "loading" "lazy") -}}
+<img
+  {{- range $k, $v := $attributes -}}
+    {{- if $v -}}
+      {{- printf " %s=%q" $k $v | safeHTMLAttr -}}
+    {{- end -}}
+  {{- end -}}>
+{{- /**/ -}}