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

apps/docs/content/(01-linear-structures)/prefix-sum/238-product-of-array-except-self.mdx

@@ -1,6 +1,7 @@
 ---
 title: '238. Product of Array Except Self'
 description: Given an integer array nums, return an array answer such that answer[i] is equal to the product of all the elements of nums except nums[i]
+icon: line-dot-left-horizontal
 sidebar:
   label: 'Product of Array Except Self'
   badge: 'Medium'

apps/docs/content/(01-linear-structures)/prefix-sum/303-range-sum-query-immutable.mdx

@@ -1,6 +1,7 @@
 ---
 title: '303. Range Sum Query - Immutable'
 description: Given an integer array nums, handle multiple queries of the following type
+icon: line-dot-left-horizontal
 sidebar:
   label: 'Range Sum Query - Immutable'
   badge: 'Easy'

apps/docs/content/(01-linear-structures)/prefix-sum/560-subarray-sum-equals-k.mdx

@@ -1,6 +1,7 @@
 ---
 title: '560. Subarray Sum Equals K'
 description: Given an array of integers nums and an integer k, return the total number of subarrays whose sum equals to k
+icon: line-dot-left-horizontal
 sidebar:
   label: 'Subarray Sum Equals K'
   badge: 'Medium'