create server-side SiteService

[sbwalker]

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[sbwalker]

• 2 different implementations of ISiteService interface (interface cannot change as modules rely on it)
• client implementation registered in client project Program.cs
• server implementation registered in server project Startup.cs
• logic from SiteController migrated to SiteService (SiteController becomes a thin API endpoint)
• HttpContextAccessor used to obtain HttpContext within SiteService
• authorization attributes need to have equivalent IsInRole() calls added to SiteService methods to ensure consistent security enforcement on server and client
• HttpContext.Response.StatusCode logic needs to remain in Controller
• Controller methods changed to asynchronous
• some Controller methods need to be refactored to integrate with results returned from SiteService
• caching migrated to SiteService so that calls originating on server will also get performance benefit
• SiteService uses Task.Run() to execute Repository methods - this is not optimal however there is significant effort to introduce a full set of new Repository async methods (the sync methods need to be retained as existing modules rely on them). Task.Run() should exhibit same performance characteristics as legacy approach as Repository has always been synchronous.