Get a random string with prefix
Examples
random_string("bucket")
#> bucketmwlefoud
replicate(10, random_string("bucket"))
#> [1] "bucketfiexombk" "bucketkeulbfdp" "bucketbcvkgufi" "bucketvjubqtaf"
#> [5] "bucketbsnaoreh" "bucketalspkcbj" "bucketcfdjagys" "bucketybhawgli"
#> [9] "bucketjbfglnew" "bucketslqexmfa"