* Updated API version package and moved attribute to each controller as it cannot be inherited.
* Ignore "$type" on types implementing interfaces in the delivery api
* Introduce root key constant
* Do not enforce ProblemDetails on every non-success response from the API + remove invalid NotFoundResult response types from various endpoints
* Update OpenAPI JSON contract to reflect the new NotFound results
* Rework language service and API
* Revert unintended commit of Directory.Build.props
* Create OS conditional test for invalid ISO codes
* Reintroduce and obsolete old Delete method on ILocalizationService + make new Delete method delete by ISO code + add obsoletion attrs to service implementation
* Review comments + utilize new Delete method
* Do not allow model reuse when creating a new language
* Fix bad merge
* Split localization service into dedicated services for language and dictionary item handling
* Replaced ILocalizationService usage in management API (as much as can be done for now)
* Ensure we can create dictionary items with explicit keys (but no duplicates)
* Fix culture controller so it works properly with pagination
* Update OpenAPI JSON
* Actually update the language being updated...
* Unit test for invalid ISO now no longer needs to differ between OS :)
* A little bit of code health improvements
* A litte less code duplication
* Remove duplicate validation
* Created a common library for the APIs and moved stuff that is required for the new content API. Also moved the versioned backoffice API route handling to the management API where it belongs.
* Remove test auth attribute from Media
