[Feature Request] Only anonymize some rows

[nigelatdas]

I want all users to be anonymized except for my companies employees.
That way they can use the same credentials in Staging as they do in Prod.

I'm thinking of some regular expression I can add as an exclude criteria when mapping emails.

[nigelatdas]

I had a go here: #107

[junkert]

This has been merged, but we will need to add testing for it. @junkert to come back and add later.