Configure mermaid to not render HTML content in diagrams

(cherry picked from commit f2e9f22f7d3d84abeea5ba2918ee5ffcc55f2dad)

Conflicts:
	app/assets/javascripts/behaviors/markdown/render_mermaid.js

app/assets/javascripts/behaviors/markdown/render_mermaid.js

@@ -25,6 +25,9 @@ export default function renderMermaid($els) {
       },
       // mermaidAPI options
       theme: 'neutral',
+      flowchart: {
+        htmlLabels: false,
+      },
     });
     $els.each((i, el) => {

changelogs/unreleased/security-mermaid-xss.yml

+---
+title: Configure mermaid to not render HTML content in diagrams
+merge_request:
+author:
+type: security