Added optional label attribute (mmistakes#3128)

Added label attribute as per utterances optional label setting.

Author: JohnScottUK

_includes/comments-providers/utterances.html

@@ -12,6 +12,7 @@
     script.setAttribute('src', 'https://utteranc.es/client.js');
     script.setAttribute('repo', '{{ site.repository }}');
     script.setAttribute('issue-term', '{{ site.comments.utterances.issue_term | default: "pathname" }}');
+    {% if site.comments.utterances.label %}script.setAttribute('label', '{{ site.comments.utterances.label }}');{% endif %}
     script.setAttribute('theme', '{{ site.comments.utterances.theme | default: "github-light" }}');
     script.setAttribute('crossorigin', 'anonymous');
 

docs/_docs/05-configuration.md

@@ -423,6 +423,7 @@ comments:
   utterances:
     theme: "github-light" # "github-dark"
     issue_term: "pathname"
+    label: "comment" # Optional - must be existing label.
 ```
 
 #### giscus comments