Boost: On premium upgrade (if image guide is enabled), request an ISA report

[dilirity]

Fixes https://github.com/Automattic/boost-cloud/issues/310

Proposed changes:

• If Image Guide is enabled after upgrading to premium and landing on the Purchase Successful page, an Image Size Analysis report will be automatically requested.

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

n/a

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

no

Testing instructions:

• Setup this version of Boost (use the free version);
• Make sure you have images on the website;
• Enable Image Guide;
• Upgrade to Premium;
• After you get redirected back to the Purchase Successful page, click continue and scroll down to the Image Size Analysis section
• There should be a report in progress (or maybe completed).

To easily test the above if you have premium, simply open /wp-admin/admin.php?page=jetpack-boost#purchase-successful. This will force the Image Size Analysis to request a report.

[github-actions]

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Boost plugin:

• Next scheduled release: August 1, 2023.
• Scheduled code freeze: July 24, 2023.

[thingalon]

The changes here look like they would work.

However, I am not sure we want to kick off a report which will generate hundreds or thousands of requests. See: https://github.com/Automattic/boost-cloud/issues/310#issuecomment-1637306125

[thingalon]

Ok, after a conversation (https://github.com/Automattic/boost-cloud/issues/310) about it, Iv'e been convinced that this will help demonstrate the value of the subscription after purchase.

[dilirity]

After merging with trunk, the linter somehow messed up and made changes to files outside this PR. Reverted the change with b2be646.

[haqadn]

Cherry-picked 9cd5215