.NET 10 Support

Support for .NET 10 has started in this pull request: #264 If you'd like to use builds of the library that support `net10.0`, you can access them through prerelease packages from feedz.io. For example in your project file: ```xml <PackageReference Include="MartinCostello.OpenApi.Extensions" Version="2.0.0-*" /> ``` and in `NuGet.config`: ```xml <?xml version="1.0" encoding="utf-8"?> <configuration> <packageSources> <add key="openapi-extensions" value="https://f.feedz.io/martincostello/openapi-extensions/nuget/index.json" /> <add key="NuGet" value="https://api.nuget.org/v3/index.json" /> </packageSources> </configuration> ``` As of preview 1, the changes of note are: 1. Dependency on Microsoft.OpenApi 2.0.0; 2. Removal of [`MapOpenApiYaml()`](https://github.com/martincostello/openapi-extensions/blob/263421e40558523ae8c68d0fe51ccda8c0fb0b52/src/OpenApi.Extensions/OpenApiEndpointRouteBuilderExtensions.cs#L39) for `net10.0` as this is now [a first-class feature of ASP.NET Core 10](https://github.com/dotnet/core/blob/main/release-notes/10.0/preview/preview1/aspnetcore.md#generate-openapi-documents-in-yaml-format).