Refactor to inherit from GraphQLHttpMiddleware

[Shane32]

Refactoring for adding/fixing these issues:

• By inheriting from GraphQLHttpMiddleware, requests now honor all of these options which were not supported previously:
  • AuthenticationSchemes
  • AuthorizedPolicy
  • AuthorizedRoles
  • AuthorizationRequired
  • DefaultResponseContentType
  • EnableBatchedRequests
  • ExecuteBatchedRequestsInParallel
  • ReadQueryStringOnPost
  • ValidationErrorsReturnBadRequest
• Moves AddGraphQLUpload to a builder method within the GraphQL namespace
• Bumps version to 4.0.0
• Built for all TFMs supported by GraphQL.Server.Transports.AspNetCore
  • .NET Framework with ASP.NET Core 2.1
  • .NET Core 2.1
  • .NET Core 3.1 and newer
• Adds license, readme and directory.props to solution
• Enable NRT annotations
• Embed readme within nuget package, configured so it displays on nuget.org
• Embed license file within nuget package
• Embed debugging symbols
• Add .NET 8.0 testing and update ci workflow
• Add error classes
• Bump GraphQL.Server.Transports.AspNetCore dependency version to 7.6.0
• Rewrite sample to use top-level statements and work for kestrel or IIS out of the box
• Removed the UserContextFactory option as this feature is already provided by GraphQL.Server via AddUserContextBuilder
• Refactored deserialization of responses to eliminate duplicated code that exists within the main GraphQL library
• Added xml comments where missing

These changes result in a net reduction of 200 lines of code.