Adopt WordPress.com connection flow from WooCommerce

[mikkamp]

User story

WooCommerce is providing a flow for connecting to the WordPress.com account from version 9.5+

Since we maintain a support policy of WooCommerce L-2 we will need to wait till at least 9.7 for it to be fully available. However we can adopt the flow already with some conditional code. Once 9.7 is available we can drop our previous flow.

Ideally we'd use this same flow for both the initial connect and in circumstances where we need to reconnect the account.

This is the followup step from removing the packages to facilitate the connection.

Additional Information

Flow details: pcShBQ-2En-p2#comment-4194
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