* Refactor jobs from HostedServices into BackgroundJobs
* Clean up generics and DI setup
* Add RecurringBackgroundJob Unit Tests
* Add ServiceCollection helper
* Add Obsolete attributes
* Add Notification Classes
* Add UnitTests for RecurringBackgroundJob HostedService
* Add NotificationEvents
* Add state to notifications
* Update UnitTests
* Add Obsolete Attributes to old hosted service classes
* Updated xmldoc in IRecurringBackgroundJob.cs
* Update Obsolete attribute messages to indicate classes will be removed in Umbraco 14
(cherry picked from commit c30ffa9ac3)
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