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

apps/docs/content/(01-linear-structures)/monotonic-stack/739-daily-temperatures.mdx

@@ -1,6 +1,7 @@
 ---
 title: '739. Daily Temperatures'
 description: Given an array of integers temperatures represents the daily temperatures, return an array answer such that answer[i] is the number of days you have to wait after the i^th day to get a warmer temperature. If there is no future day for which this is possible, keep answer[i] == 0 instead
+icon: line-dot-left-horizontal
 sidebar:
   label: 'Daily Temperatures'
   badge: 'Medium'

apps/docs/content/(01-linear-structures)/monotonic-stack/853-car-fleet.mdx

@@ -1,6 +1,7 @@
 ---
 title: '853. Car Fleet'
 description: There are n cars at given miles away from the starting mile 0, traveling to reach the mile target
+icon: line-dot-left-horizontal
 sidebar:
   label: 'Car Fleet'
   badge: 'Medium'