Obfuscates a string by returning a new string of 8 characters. If the input
string is longer than 10 characters and show_tail is True, then up to 4 of
its final characters will become final characters of the obfuscated string;
all other characters are ”*”.“abc” -> ""
“abcdefgh” -> ""
“abcdefghijk” -> “*******k”
“abcdefghijklmnopqrs” -> “****pqrs”