Add Redactable

[garethrees]

Relevant issue(s)

• Supersedes [#8823] Redactable #9319
• Prep for Admin UI showing which where redactions are applied and redactions apply to what #8823
• Prep for Ability for censor rules to be applied on a per-role basis #8824
• Requires [#8823] Make CensorRule polymorphic & refactor #9302

What does this do?

Adds explicit interfaces for getting redacted/unredacted versions of content

Why was this needed?

• Make it easier to get different versions of content
• Reduce number of methods / method overrides that currently do the above
• Protects against information leaks by forcing developers to explicitly permit unredacted access to data

Implementation notes

Here's how this will work:

class User < ApplicationRecord
  include Redactable
  redactable :from_name
end

user.censor_rules.create!(
  text: 'Bob Smith',
  replacement: '[name removed]',
  last_edit_editor: 'x',
  last_edit_comment: 'x'
)

msg = user.info_requests.first.outgoing_messages.first

msg.from_name
# => "[name removed]"

msg.unredacted.from_name
# => "Bob Smith"

Notes to reviewer

While this does force explicit unredacted permission, it still requires us to remember to add attributes to redactable. There's an alternative version of this where we by default assume attributes will hold PII unless explicitly told they won't, but that feels like it would get a bit too annoying?

At the moment this applies both censor rules and text masks. We may want to split these up so that we can do e.g. (record.censored.unmasked.foo).

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