Issue #3504910: Add webp as available image extension

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Closes #3504910

src/Entity/SectionLibraryTemplate.php

@@ -198,7 +198,7 @@ class SectionLibraryTemplate extends ContentEntityBase implements SectionLibrary
       ->setSettings([
         'uri_scheme' => 'public',
         'file_directory' => 'section_library',
-        'file_extensions' => 'gif png jpg jpeg',
+        'file_extensions' => 'gif png jpg jpeg webp',
       ])
       ->setDisplayOptions('view', [
         'label' => 'hidden',