email constants

add mailchimp transactional last to pecking order

beginnings of dispatcher

adds messagingservice detail

adds validation option

adds test fixture

lint

adds correct typing

update tests

return types back to how they were but manually coerce

adds migration to add MAILCHIMP_TRANSACTIONAL to enum

add secrets validation

add missing values

adds acceptable details schema to API input

refine dispatch logic

adds secrets to docs

remove unused

test for creating a mailchimp transactional connector

test for configuring mailchimp transactional secrets

adds type-ignore and corrects handler types

Merge branch 'main' into sp/2737/mailchimp-transactional-email

bump downrev

use Callable not function

update test

update test data

remove ref to non existant fixture

fix nits, update changelog