Do not allow SVG by default (#3640)

src/components/ha-markdown.ts

@@ -10,6 +10,7 @@ let worker: any | undefined;
 @customElement("ha-markdown")
 class HaMarkdown extends UpdatingElement {
   @property() public content = "";
+  @property({ type: Boolean }) public allowSvg = false;
 
   protected update(changedProps) {
     super.update(changedProps);
@@ -22,11 +23,17 @@ class HaMarkdown extends UpdatingElement {
   }
 
   private async _render() {
-    this.innerHTML = await worker.renderMarkdown(this.content, {
-      breaks: true,
-      gfm: true,
-      tables: true,
-    });
+    this.innerHTML = await worker.renderMarkdown(
+      this.content,
+      {
+        breaks: true,
+        gfm: true,
+        tables: true,
+      },
+      {
+        allowSvg: this.allowSvg,
+      }
+    );
 
     this._resize();