[Backport] Reformat release notes generation (#3759)

This PR backports small reformatting of the release notes templates.

scripts/release/build-changelogs.sh

@@ -48,6 +48,7 @@ for audience in "${audiences[@]}"; do
     echo "Processing audience: $audience ($audience_id)"
     export TARGET_AUDIENCE=$audience
     tera -t "${TEMPLATE_AUDIENCE}" --env --env-key env "${CONTEXT_JSON}" > "$OUTPUT/relnote_${audience_id}.md"
+    cat "$OUTPUT/relnote_${audience_id}.md" >> "$OUTPUT/relnote_combined.md"
 done
 
 # Show the files

scripts/release/templates/audience.md.tera

-## Release {{ env.PRODUCT }} {{ env.VERSION }}
-
-Changelog for `{{ env.TARGET_AUDIENCE }}`.
+### Changelog for `{{ env.TARGET_AUDIENCE }}`
 
 {% for file in prdoc -%}
-#### PR #{{file.doc_filename.number}}: {{ file.content.title }}
 {% for doc_item in file.content.doc %}
 {%- if doc_item.audience == env.TARGET_AUDIENCE %}
+#### [#{{file.doc_filename.number}}]: {{ file.content.title }}
 {{ doc_item.description }}
 {% endif -%}