feat: add PR link support in changelog updates

pr_agent/settings/pr_update_changelog_prompts.toml

@@ -5,6 +5,9 @@ Your task is to add a brief summary of this PR's changes to CHANGELOG.md file of
 - Only add new changes (don't repeat existing entries)
 - Be general, and avoid specific details, files, etc. The output should be minimal, no more than 3-4 short lines.
 - Write only the new content to be added to CHANGELOG.md, without any introduction or summary. The content should appear as if it's a natural part of the existing file.
+{%- if pr_link %}
+- If relevant, convert the changelog main header into a clickable link using the PR URL '{{ pr_link }}'. Format: header [*][pr_link]
+{%- endif %}
 
 
 {%- if extra_instructions %}