Boost: Backport 4.5.1 release changes

[dilirity]

Fixes HOG-374

Proposed changes:

• Backport changes from the beta release;
• Update stable tag to 4.5.1.

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

HOG-374

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

no

Testing instructions:

• Make sure all GitHub checks pass;
• Proof read changes and make sure they make sense.

[github-actions]

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[jp-launch-control]

Code Coverage Summary

This PR did not change code coverage!

That could be good or bad, depending on the situation. Everything covered before, and still is? Great! Nothing was covered before? Not so great. 🤷

Full summary · PHP report · JS report