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

apps/docs/content/(01-linear-structures)/binary-search/704-binary-search.mdx

@@ -1,6 +1,7 @@
 ---
 title: '704. Binary Search'
 description: Given an array of integers nums which is sorted in ascending order, and an integer target, write a function to search target in nums. If target exists, then return its index. Otherwise, return -1
+icon: line-dot-left-horizontal
 sidebar:
   label: 'Binary Search'
   badge: 'Easy'