Make "what's new" available before update, allow opt out, facilitate cherry-picking

[microshnik]

Given the difficulty of version roll-back, it would be very helpful to know before an update happens what we should expect to change, and also to have the option to delay the update indefinitely (without constant nagging!) if it appears disruptive (a la the 157 "visual refresh").  Bug fixes and security patches need not be disclosed, but new features and changes to existing behavior should be enumerated, including any applicable settings/configs for reverting/disabling these changes.  Anything configurable should also be presented to the user in a page or popup immediately before and after the update to streamline getting back to normal.  It should go without saying that anything I've mentioned here for before an update is contingent upon the setting for having updates not be applied automatically, but the display of configs relevant to the update should always be included in the "What's New" post-update page.

[kelimuttu]

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