refactor: image handling logic + support for external images (#1235)

* refactor: simplify image partial logic, remove generation of different image sizes

* Remove `defaultImage.opengraph` configuration from `params.toml`.

layouts/_partials/article/components/header.html

@@ -1,34 +1,12 @@
 <header class="article-header">
-    {{- $image := partialCached "helper/image" (dict "Context" . "Type" "article") .RelPermalink "article" -}}
-    {{ if $image.exists }}
-        <div class="article-image">
-            <a href="{{ .RelPermalink }}">
-                {{ if $image.resource }}
-                    {{- $Permalink := $image.resource.RelPermalink -}}
-                    {{- $Width := $image.resource.Width -}}
-                    {{- $Height := $image.resource.Height -}}
-                    {{- $Srcset := "" -}}
-                    
-                    {{- if (default true .Page.Site.Params.imageProcessing.cover.enabled) -}}
-                        {{- $thumbnail := $image.resource.Resize "800x" -}}
-                        {{- $thumbnailRetina := $image.resource.Resize "1600x" -}}
-                        {{- $Srcset = printf "%s 800w, %s 1600w" $thumbnail.RelPermalink $thumbnailRetina.RelPermalink -}}
-                        {{- $Permalink = $thumbnail.RelPermalink -}}
-                        {{- $Width = $thumbnail.Width -}}
-                        {{- $Height = $thumbnail.Height -}}
-                    {{- end -}}
-
-                    <img src="{{ $Permalink }}"
-                        {{ with $Srcset }}srcset="{{ . }}"{{ end }}
-                        width="{{ $Width }}" 
-                        height="{{ $Height }}" 
-                        loading="lazy"
-                        alt="Featured image of post {{ .Title }}" />
-                {{ else }}
-                    <img src="{{ $image.permalink }}" loading="lazy" alt="Featured image of post {{ .Title }}" />
-                {{ end }}
-            </a>
-        </div>
+    {{- $image := partial "helper/image" (dict "Image" .Params.image "Resources" .Resources) -}}
+    {{ if $image }}
+    <div class="article-image">
+        <a href="{{ .RelPermalink }}">
+            <img src="{{ $image.Permalink }}" width="{{ $image.Width }}" height="{{ $image.Height }}" loading="lazy"
+                alt="Featured image of post {{ .Title }}" />
+        </a>
+    </div>
     {{ end }}
 
     {{ partialCached "article/components/details" . .RelPermalink }}