Enhancement: Add leading zero for easier file navigation

[Ninzero]

This PR follows https://github.com/LeetCode-OpenSource/vscode-leetcode/pull/582 Hard code leading zero is not a great idea, we should let user decide whether to add leading zeros or not. Since id now is four digits at most, and it is not likely that we are going to see 5 digits ids in the near future. I don't think implement grammars like ${id%05d} is necessary. So I just hard code it to 4 digits.