How to specify "hosting startup assemblies" via code using the "minimal hosting model"?

Please describe **if and how** you can set hosting startup assemblies in the code when using the new "minimal hosting model" of ASP.NET Core 6.0 and higher.

Or give a hint to https://github.com/dotnet/aspnetcore/issues/38765

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* ID: 613ad64e-bc62-edf7-2e86-42210de718f4
* Version Independent ID: aabbbc32-3237-5ef9-c422-892dc6884a22
* Content: [Use hosting startup assemblies in ASP.NET Core](https://learn.microsoft.com/en-us/aspnet/core/fundamentals/host/platform-specific-configuration?view=aspnetcore-7.0#specify-the-hosting-startup-assembly)
* Content Source: [aspnetcore/fundamentals/host/platform-specific-configuration.md](https://github.com/dotnet/AspNetCore.Docs/blob/main/aspnetcore/fundamentals/host/platform-specific-configuration.md)
* Product: **aspnet-core**
* Technology: **aspnetcore-fundamentals**
* GitHub Login: @tdykstra
* Microsoft Alias: **riande**