CORE-2674 Creates a new company setting for marketing emails that determines whether an option should be displayed for users to opt-in, and how the option works.

Per CORE-2674 the way opt-in/opt-out actually work will be defined by the Order Settings

The Order plugin needs to be updated to observe this setting, and display or not display a marketing email opt-in option that if displayed will either be checked or not checked by default based on the company setting.

The field should be displayed where the Terms are displayed if enabled (if those are enabled for the order form) which is right after the account is created, before clicking to checkout & pay. UNLESS the setting was previously defined, because they purchased something prior.

Add a new section after Authentication when creating a new client account called "Additional Options", and put the opt-in checkbox here. It should appear between the Authentication section and the submit button.

There's already an Additional Settings section, instead put this at the bottom above the "Create Account" button, potentially in a well.

Display the option below "I have read and agree to the Terms and Conditions"