Add a way to customize WebApplicationBuilder before Build is called

## Background and Motivation

Before the Minimal API there was [`IStartupFilter`](https://learn.microsoft.com/en-us/dotnet/api/microsoft.aspnetcore.hosting.istartupfilter?view=aspnetcore-6.0) interface that allowed us to customize existing `IApplicationBuilder`. But I can't find something similar for `WebApplicationBuilder`.

It would be really useful to have such an option. For example, `WebApplicationBuilder.Logging` immediately executes provided code, so it is impossible to use configuration sources or other services that can be added later.

As I found, Serilog developers faced the same issue [here](https://github.com/serilog/serilog-aspnetcore/blob/bf4ae072f7472d285c72f9a43f3eb4920e743110/src/Serilog.AspNetCore/SerilogWebHostBuilderExtensions.cs#L100): instead of simple calling `WebApplicationBuilder.Logging.AddProvider` they have to do lazy initialization via `ConfigureServices.AddSingleton(SerilogFactory)` and moreover implement their own `ILoggerFactory` for that.

Same thoughts may be also applied for `WebApplication`.

## Proposed API

Add startup filters for `WebApplicationBuilder` and `WebApplication`:

```csharp
public interface IWebApplicationBuilderStartupFilter
{
Action Configure(Action next);
}

public interface IWebApplicationStartupFilter
{
Action Configure(Action next);
}
```

## Usage Examples

```csharp
public class WebApplicationBuilderStartupFilter : IWebApplicationBuilderStartupFilter
{
public Action Configure(Action next)
{
return builder =>
{
var someRequiredColdLogSettings = builder.Configuration.Get();

builder.Logging.AddProvider(new MyLoggerProvider(someRequiredColdLogSettings));

next(builder);
};
}
}
```

## Alternative Designs

Instead of some startup filters there may be some pre build/run actions.

## Risks

I'm not an expert of AspNetCore, so if there is another way to solve my issue please tell me.