Implement new backoffice upgrader

[nikolajlauridsen]

This is a continuation of #12790.

This implements the versions upgrades, there's not an awful lot to mention here that's not already mentioned in #12790, so read that for more information.

The only thing really worth mentioning is that authorizing (starting) the upgrade used to be part of the InstallApiController, this is now its own controller UpgradeController

Testing

Just like #12790, you must add this to Umbraco.Cms.csproj and Umbraco.Web.BackOffice.csproj

<ProjectReference Include="..\Umbraco.Cms.ManagementApi\Umbraco.Cms.ManagementApi.csproj" />

Other than that add a migration to enter the upgrade runtime state, and test away.