This function increments a string, to create a new string.
If the string already ends with a number, the number should increment by 1. If the string does not end with a number. the number 1 should appended to the new string. If the number has leading zeros the amount of digits is considered.
Examples:
foo -> foo1
foobar23 -> foobar24
foo0042 -> foo0043
foo9 -> foo10
foo099 -> foo100