Input validation: Configuration Wizard

[afercia]

See https://github.com/Yoast/wordpress-seo/issues/12173.

All the Configuration Wizard inputs that require a specific format should use an input validation mechanism and provide proper feedback to users.

For the Social Accounts URL fields, there's a PR exploring browsers constraint validation, see #827.

Other fields that need some input validation mechanism:

Google authorization code:

• it is currently possible to enter any value
• no feedback is given
• it is possible to move to the next step even after entering a clearly invalid value

Newsletter email:

• the entered value is validated, however the feedback is insufficient
• the item in error is not clearly identified
• the item in error is not styled
• it is possible to move to the next step even after entering a clearly invalid value
• important: the messages come from the Mailchimp API and are not translated

Good news:

• the visible message area is an ARIA live region so error (and success) messages are announced to assistive technologies
• there are proper suggestions for correction

Not translated messages:

[jdevalk]

I see three different issues here:

• Google authorization I don't really care about this one for now, for all sorts of reasons, happy to explain on Slack.
• MailChimp error positioning Seems like we should move that error slightly and make it a bit easier to understand what it relates to, as well as style the input field on error.
• MailChimp error translation We should see whether we can (automatically and hidden) specify a form language based on the user language in the MailChimp form, as I think MailChimp does have translated error messages available.

[afercia]

Closing in favor of https://github.com/Yoast/javascript/issues/137 and https://github.com/Yoast/javascript/issues/138