feat(plugins/leetcode): add plugin (#1213) [skip ci]

source/plugins/leetcode/queries/skills.graphql

@@ -0,0 +1,18 @@
+query Skills ($username: String!) {
+  matchedUser(username: $username) {
+    tagProblemCounts {
+      advanced {
+        tagName
+        problemsSolved
+      }
+      intermediate {
+        tagName
+        problemsSolved
+      }
+      fundamental {
+        tagName
+        problemsSolved
+      }
+    }
+  }
+}