Add canonical e-mail blocks for suspended accounts (#16049)

Prevent new accounts from being created using the same underlying
e-mail as a suspended account using extensions and period
permutations. Stores e-mails as a SHA256 hash

app/models/canonical_email_block.rb

@@ -0,0 +1,27 @@
+# frozen_string_literal: true
+# == Schema Information
+#
+# Table name: canonical_email_blocks
+#
+#  id                   :bigint(8)        not null, primary key
+#  canonical_email_hash :string           default(""), not null
+#  reference_account_id :bigint(8)        not null
+#  created_at           :datetime         not null
+#  updated_at           :datetime         not null
+#
+
+class CanonicalEmailBlock < ApplicationRecord
+  include EmailHelper
+
+  belongs_to :reference_account, class_name: 'Account'
+
+  validates :canonical_email_hash, presence: true
+
+  def email=(email)
+    self.canonical_email_hash = email_to_canonical_email_hash(email)
+  end
+
+  def self.block?(email)
+    where(canonical_email_hash: email_to_canonical_email_hash(email)).exists?
+  end
+end