Marketing email promotions

[dblatcher]

What does this change?

• Add a new block element "MarketingEmailSignupBlockElement" that can be added to an article as part of the enhancement function to include a promotion for a marketing email.
• creates a component MarketingEmailSignUpWrapper to represent the element - mostly using the same sub-components at the existing EmailSignUpWrapper - but rendering a link to the mma /email-prefs page instead of a sign-up form.
• adds an "emailType" prop to the sign-up subcomponents to allow for the variations in behaviour and presentation between MarketingEmailSignUpWrapper and EmailSignUpWrapper
• extends the enhanceNewsletterSignup function to check for tags corresponding to marketing emails and insert a "MarketingEmailSignupBlockElement"
• defines a list of MarketingConsentEmail representing those hard-coded into the identity repo

This PR would currently have no user-facing effects as non of the defined MarketingConsentEmail have the "promotionTagId" property.

Why?

There's a long-standing request from the Guardian jobs team in-article promotions for the Guardian Job marketing email, that would work in substantially the same way as the existing sign-up blocks for editorial newsletters ie:

• The promotion is added to an article using a tag (in the case of editorial newsletters, tags with an id starting "campaign/email" are used)
• If the article is supposed to promote the email, a sign-up block is placed in the article body

This PR provides a mechanism to allowing that - when a tag is created to promote a marketing email, its Id can be added to the object describing the email in DCR.

Future work

• get design, compliance, marketing input on the new element - it is currently modelled on the editorial newsletter block, but there may be a desire for something more distinct
• PR in frontend to support the new form of sign-up request to the API
• add the tag ids to the list of MarketingConsentEmails when a pattern/convention is agreed (these are likely to be campaign tags of some sort rather than existing keyword or sectioning tags)

Screenshots

Before	After