Implement "Email Verification Code" workflow

As a part of this rollout users will sometimes be prompted to receive a verification code to their specified email address before being permitted to sign-in. Refer to that readiness issue for some context into the criteria that defines this behaviour.

In recent weeks (as of 2023-11-20), there seems to have been a significant climb in the number of tickets relating to this coming through. See this Zendesk query for an example. though keep in mind this can be intermixed with legitimate 2FA requests.

For the month of October, 2023

TICKETS	search
70	form:"SaaS Account" "verification code" created>2023-09-30 -"2FA" created<2023-11-01
49	form:"SaaS Account" "verification code" created>2023-09-30 created<2023-11-01 tags:free_customer -"2FA"

For the month of November, 2023 to-date (2023-11-20)

TICKETS	search
62	form:"SaaS Account" "verification code" created>2023-10-31 -"2FA"
48	form:"SaaS Account" "verification code" created>2023-10-31 tags:free_customer -"2FA"

We should enable a workflow that clearly covers:

• What logs to check
  • Kibana
  • Mailgun
• What information we can or should share with a customer
• Any macros we should write
• Any troubleshooting that Support can take, if any, to move the ticket along.

We could also expand this into Phone/SMS verification (via the Tele provider), as it would have similar steps.