Jetpack: Add coupon event properties to My Plan Partner Banner component

[kallehauge]

Changes proposed in this Pull Request:

Add a coupon event property to <MyPlanPartnerCoupon> so we can differentiate partners:

• Add a new coupon event property to <MyPlanPartnerCoupon>.
• Allow for new optional event property in <MyPlanBanner>.

Jetpack product discussion

• @jeherve suggested adding these properties over at Jetpack plugin: add Jetpack partner coupon banner on My Page #22633 (comment)

Does this pull request change what data or activity we track or use?

This PR adds a new property to two new events:

• jetpack_wpa_click (we trigger a WPA click event when the banner button is clicked):
  • coupon: The coupon the user is about to claim.
• jetpack_my_plan_banner_view (will be trigger each time a My Plan banner is viewed):
  • coupon: The coupon the user is about to claim.

Testing instructions:

• Spin up this branch locally or as a JN beta site.
• Create a Jetpack connection.
• Go to /wp-admin/admin.php?jetpack-partner-coupon={COUPON}.
  • ^ Replace {COUPON} with the coupon found here: 2b922-pb.
• Go to Jetpack > My Plan
• If you click the Redeem button, you should be redirected to checkout.
• Hopefully, you've both seen the banner and clicked the Redeem button by now, which means you have triggered both events mentioned in the tracking section above.
• It will take 5-10min for the data to show up in the live data (documented here: PCYsg-4KT-p2), so go grab a ☕ - you deserve it!

[github-actions]

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Jetpack plugin:

• Next scheduled release: March 1, 2022.
• Scheduled code freeze: February 22, 2022.

[jeherve]

This tests well for me, thank you!