* Revert "v14: Remove mentions of UmbracoApiController (#15863)"
This reverts commit 30e2dea57a.
* Obsolete UmbracoApiController
* Added a few more obsoletion messages
* Removed some of the reintroduced stuff again
* Add obsoletion to FrontEndRoutes controller
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Co-authored-by: kjac <kja@umbraco.dk>