automatic_updates 8.x-2.0-beta4

Another day, another beta.

This release does a lot of refactoring and fixes several bugs found during beta testing at DrupalCon Portland. Thanks again to all the people who tested it, and submitted excellent bug reports!

We've continued refinining Package Manager's API, especially its boundaries and edge case handling, and strive to make it behave as clearly and consistently as possible. We're excited to see what gets built on top of it! (Looking at you, Project Browser...)

Issues fixed in this release:

#3277817: Before applying the update, don't show the checkbox for maintenance mode if the site is already in maintenance mode
#3271235: If there are no supported updates, but there are other updates, link to the available updates page
#3277235: Package Manager's help text should provide a PHP snippet for setting the path to Composer in settings.php
#3277014: Increase timeouts during create and apply
#3278411: Always use FileSystemInterface::getTempDirectory() to get the temporary directory
#3280180: Consolidate all version validation logic into a single class
#3279733: \Drupal\automatic_updates\ProjectInfo::getInstallableReleases() will return releases lower than the installed version if the installed version is a dev release
#3280923: CronUpdater::begin() should throw an exception of if cron updates are disabled
#3276031: Create installed version validator
#3276662: Add test coverage for the fix in #3276661
#3279229: StagedProjectsValidatorTest should use a virtual project
#3279086: StagedDatabaseUpdateValidatorTest should use a virtual project
#3279064: Consolidate logic around test stages
#3280204: Missing documentation on 'addError' and 'add Warning'
#3277229: Auto-wire Composer Stager into Package Manager
#3279527: Ensure plugins are reloaded after an update
#3278435: Make Stage::getStagingRoot() private
#3275316: Change AutomaticUpdatesKernelTestBase::setReleaseMetadata() to return metadata for different projects based on request path
#3274047: Do not use rootUser in tests unless absolutely necessary
#3281405: Add @internal to Automatic Updates validator classes