Issue #3189129 by swentel: Add a notifications channel

README.md

src/Commands/ActivityPubCommands.php

src/Entity/ActivityPubActor.php

src/Entity/Storage/ActivityPubActivityStorage.php

src/Form/ActivityPubSettingsForm.php

src/Plugin/activitypub/type/Core.php

src/Services/Reader.php

src/Services/Type/TypePluginBase.php

tests/src/Functional/FollowTest.php