docs(docs): add page icon frontmatter to problem pages

apps/docs/content/(03-hierarchical)/heap-priority-queue/973-k-closest-points-to-origin.mdx

@@ -1,6 +1,7 @@
 ---
 title: '973. K Closest Points to Origin'
 description: Given an array of points where points[i] = [xi, yi] represents a point on the X-Y plane and an integer k, return the k closest points to the origin (0, 0)
+icon: line-dot-left-horizontal
 sidebar:
   label: 'K Closest Points to Origin'
   badge: 'Medium'