feat: icons for highlight shortcode (#169)

## Description

i´ve added icons for the highlight shortcode. it appears next to the
roofline text.
i´m not entirely sure, if these icons are 100% appropriate, so please
suggest others if you can think of any :)

## Checklist
<!-- Check fields with: [x] / Abhaken von Punkten: [x] -->

- [ ] Check the License of new pictures (non-commercial use without
attribution) <!-- Die Lizenz neuer Bilder geprüft (nicht-kommerzielle
Nutzung ohne Namensnennung) -->

The content was modified in the following languages: <!-- Der Inhalt
wurde für die folgenden Sprachen angepasst -->
- [ ] English
- [ ] German

Co-authored-by: Lennart Rommeiss <61516567+lenderom@users.noreply.github.com>

Author: therobrob

assets/sass/textHighlight.scss

@@ -12,6 +12,9 @@
   text-transform: uppercase;
   font-weight: bold;
   opacity: .8;
+  display: flex;
+  align-items: center;
+  gap: .4rem;
 }
 
 .m-text-highlight--tip {

layouts/shortcodes/highlight.html

@@ -1,7 +1,11 @@
 {{- $param := .Get 0 -}}
+{{ $iconMapping := dict "important" "error" "inofficial" "warning" "tip" "lightbulb_2" }}
+
 <div class="m-text-highlight m-text-highlight--{{ $param }}">
     {{- if $param -}}
-    <div class="m-text-highlight__roofline">{{ T (printf "highlight.%s" $param) }}</div>
+    <div class="m-text-highlight__roofline">
+        {{- partial "icon" (index $iconMapping $param) -}}
+        {{ T (printf "highlight.%s" $param) }}</div>
     {{- end -}}
     <div>
 {{ .Inner }}