[TASK] Add alias for code language "rst" to "plaintext" (#209)

To avoid warnings when rendering the docs until the `highlight.php`
language for restructured text is available.

Related: #173

Author: brotkrueml

packages/typo3-docs-theme/resources/config/typo3-docs-theme.php

@@ -40,6 +40,7 @@
         ->set(CodeHighlight::class)
         ->arg('$languageAliases', [
             'none' => 'plaintext',
+            'rst' => 'plaintext',
             'text' => 'plaintext',
         ])
         ->arg('$additionalLanguages', [