Connection: send package versions on init hook

[kbrown9]

Fixes #21165

Changes proposed in this Pull Request:

• Send the package versions to wpcom on the init hook instead of plugins_loaded to prevent a conflict with a third party plugin. The plugin isn't ready until the after_setup_theme action has fired.

• Is there any reason that we shouldn't move the package version check and wpcom request to the init hook? This seems like a safe change to me.

Jetpack product discussion

• n/a

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

• no

Testing instructions:

1. On a brand new site, install the Passwords Evolved plugin.
2. Then, install, activate, and connect Jetpack version 10.0.
3. Then, change from 10.0 to this branch.
4. Verify that no fatal errors occur.
5. Verify that the jetpack_package_versions option has been set: wp option get jetpack_package_versions

[test-case-reminder]

Here are some suggested test cases for this PR.

Connection

• In-place connection with free plan
• In-place connection with paid plan
• In-place connection with product purchase
• Classic connection. Use Safari, or set a constant JETPACK_SHOULD_NOT_USE_CONNECTION_IFRAME to true
• Disconnect/reconnect connection
• Secondary user connection
• Connection on multisite

Verify that the changes are compatible with the plugins that use the connection package.

• WooCommerce Payments
• Jetpack Boost
• Previous versions of Jetpack

If you think that suggestions should be improved please edit the configuration file here. You can also modify/add test-suites to be used in the configuration file.

[github-actions]

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[kraftbj]

@kbrown9 Following up -- could we set this even later? I noticed while testing Jetpack on a site that this API call added about a half-second to the execution time and, as far as I can tell, it isn't providing benefit to the visitor. Could we add this to just shutdown?