Duplicate root account email addresses can be generated

[sengi]

For example, in alphagov/aws-billing-account#363 and alphagov/aws-billing-account#364 co-special-advisors-portal-production and co-special-advisors-portal-preproduction both got automatically shortened to aws-root-accounts+co-sp-ad-po-pr. Terraform then fails to create the second of the two accounts because its root account email address clashes with the first.

One fix that springs to mind is to have the re-request-an-aws-account bot search the list of existing names and replace the last character with a 1, or if that's taken then a 2, etc. to ensure uniqueness.