Your job is to write a function called increment_string which increments a string, to create a new string. If the string already ends with a number, the number should be incremented by 1. If the string does not end with a number the number 1 should be appended to the new string.
Examples:
"foo" -> "foo"
"foobar23" -> "foobar24"
"foo0042" -> "foo0043"
"foo9" -> "foo10"
"foo099" -> "foo100"
Attention: If the number has leading zeros the amount of digits should be considered.