Rename Project Euler directories and other dependent changes (#3300)

* Rename all Project Euler directories:

Reason:
The change was done to maintain consistency throughout the directory
and to keep all directories in sorted order.

Due to the above change, some config files had to be modified:
'problem_22` -> `problem_022`

* Update scripts to pad zeroes in PE directories

project_euler/problem_004/sol2.py

@@ -0,0 +1,32 @@
+"""
+Problem:
+A palindromic number reads the same both ways. The largest palindrome made from
+the product of two 2-digit numbers is 9009 = 91 x 99.
+
+Find the largest palindrome made from the product of two 3-digit numbers which
+is less than N.
+"""
+
+
+def solution(n: int = 998001) -> int:
+    """Returns the largest palindrome made from the product of two 3-digit
+    numbers which is less than n.
+
+    >>> solution(20000)
+    19591
+    >>> solution(30000)
+    29992
+    >>> solution(40000)
+    39893
+    """
+    answer = 0
+    for i in range(999, 99, -1):  # 3 digit numbers range from 999 down to 100
+        for j in range(999, 99, -1):
+            product_string = str(i * j)
+            if product_string == product_string[::-1] and i * j < n:
+                answer = max(answer, i * j)
+    return answer
+
+
+if __name__ == "__main__":
+    print(solution(int(input().strip())))