Multi-factor authentication (#1817)

* Initial pass

* Tests for MFA and locale cleanup

* Brakeman

* Update two-factor authentication status styling

* Update app/models/user.rb

Co-authored-by: Zach Gollwitzer <zach@maybe.co>
Signed-off-by: Josh Pigford <josh@joshpigford.com>

* Refactor MFA verification and session handling in tests

---------

Signed-off-by: Josh Pigford <josh@joshpigford.com>
Co-authored-by: Zach Gollwitzer <zach@maybe.co>

app/views/mfa/verify.html.erb

@@ -0,0 +1,14 @@
+<%
+  header_title t(".title")
+  header_description t(".description")
+%>
+
+<%= styled_form_with url: verify_mfa_path, method: :post, class: "space-y-4" do |form| %>
+  <%= form.text_field :code,
+    required: true,
+    autofocus: true,
+    autocomplete: "one-time-code",
+    label: t(".page_title") %>
+
+  <%= form.submit t(".verify_button") %>
+<% end %>