Fix/payments correct link to setup plans

[simison]

Resolves #38766

Links opening payment setup for Jetpack & WP.com sites now open to wordpress.com/earn/ for everyone. This changes Jetpack sites to go for Jetpack Cloud version instead.

Proposed changes:

• Link to Jetpack Cloud for Monetize UI for Jetpack sites

Other information:

• Have you written new tests for your changes, if applicable?
• Have you checked the E2E test CI results, and verified that your changes do not break them?
• Have you tested your changes on WordPress.com, if applicable (if so, you'll see a generated comment below with a script to run)?

Jetpack product discussion

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

Testing instructions:

• Add subscribe block; "setup plan" should bring you to Jetpack Cloud from Jetpack site.
• Sync PR to WP.com, and try the block there. You should end up in Monetize dash in Calypso blue.
• See Jetpack -> Settings -> Earn, and all setup links now point to Jetpack Cloud. This UI is just for Jetpack sites.

[github-actions]

Are you an Automattician? Please test your changes on all WordPress.com environments to help mitigate accidental explosions.

• To test on WoA, go to the Plugins menu on a WordPress.com Simple site. Click on the "Upload" button and follow the upgrade flow to be able to upload, install, and activate the Jetpack Beta plugin. Once the plugin is active, go to Jetpack > Jetpack Beta, select your plugin, and enable the fix/payments-correct-link-to-setup-plans branch.

• To test on Simple, run the following command on your sandbox:

  bin/jetpack-downloader test jetpack fix/payments-correct-link-to-setup-plans
  

Interested in more tips and information?

• In your local development environment, use the jetpack rsync command to sync your changes to a WoA dev blog.
• Read more about our development workflow here: PCYsg-eg0-p2
• Figure out when your changes will be shipped to customers here: PCYsg-eg5-p2

[github-actions]

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[simison]

There are "untangled" sites among WP.com sites which should also get redirected to JP cloud, but we can look into those separately.

[jeherve]

This may be a good opportunity to move away from location.hostname, which won't return the correct information on sites that live in a subdirectory.

Could we rely on getRedirectUrl() here maybe?

[simison]

Looks like a combo of getRedirectUrl() and getSiteFragment() would be best, and there are other places with /earn links where this is needed. Like Donations block.

[pkuliga]

It seems it contains more fixes, not only for the "Set up a paid plan" link.

Can you add some testing instructions to make it clear how to test it?