Upgrade/Install: Allow for WordPress.org to remotely disable auto-updates for plugins/themes

As auto-updates are rolled out across WordPress.org, the API response can modulate the response, ensuring that a rolled out could be stalled or staggered if needed for security or performance reasons.

This brings the changes from [48701] to the 5.5 branch.

Fixes #50824.
Props dd32, whyisjake, SergeyBiryukov.

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git-svn-id: https://core.svn.wordpress.org/branches/5.5@48464 1a063a9b-81f0-0310-95a4-ce76da25c4cd