Feature request: Iteration count on fingerprint

[jeremyforan]

As we utilize the fingerprinting to protect PII it would be ideal if we could include a work factor/iteration into the fingerprint plugin:

with user_password = "password" you currently get "203f495c364d4bc6b7111e82ce0cc88d" as the result

You could add 'iterations' as an integer that would rehash the output n amount of times with the default being 1.

fingerprint {
method => "MD5"
key => "saltandpepper"
source => "user_password"
target => "hashed_password"
iterations => 4
}

The output for "password" would be "7a8b540841db8efae6a8ebac88aa39e4" as oppossed to "203f495c364d4bc6b7111e82ce0cc88d"

The is in line with data privacy best practices. It also won't break any current configs.