Boost: Add tests for Image CDN

[dilirity]

Part of #33877

Proposed changes:

• Add e2e tests for the Image CDN module:
  • Upgrade section isn't visible while the module is inactive;
  • Image isn't loaded via CDN while the module is inactive;
  • Upgrade section is visible while the module is active;
  • Image is loaded via CDN when module is active.
• Update Boost CLI to support activating/deactivating Image CDN;
• Update docker e2e test matrix to include tests (you can check the GH actions section to see the tests).

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:

• Run tests to see if everything is working as expected.

[github-actions]

Thank you for your PR!

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Boost plugin:

• Next scheduled release: May 7, 2024.
• Scheduled code freeze: April 29, 2024.

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[haqadn]

Nice 👍🏼

[dilirity]

@haqadn this needs a review, since I merged it with trunk after #36716 got merged.

[haqadn]

👍🏼