[API Proposal]: Add support for `HostApplicationBuilder` in AmbientMetadata extension

[julealgon]

Background and motivation

The Microsoft.Extensions.AmbientMetadata has a UseApplicationMetadata that currently targets the old IHostBuilder interface:

extensions/src/Libraries/Microsoft.Extensions.AmbientMetadata.Application/ApplicationMetadataHostBuilderExtensions.cs

Line 26 in 6eb7ad8

public static IHostBuilder UseApplicationMetadata(this IHostBuilder builder, string sectionName = DefaultSectionName)

I would like to propose the creation of a version of this method that targets IHostApplicationBuilder instead, which is the more modern, property-based hosting API.

API Proposal

public static class ApplicationMetadataHostApplicationBuilderExtensions
{
    public static IHostApplicationBuilder UseApplicationMetadata(this IHostApplicationBuilder builder);
}

API Usage

var builder = WebApplication.CreateBuilder(args);

builder.UseApplicationMetadata();

// ...

var app = builder.Build();

// ,,,

await app.RunAsync();

Alternative Designs

Methods that work directly on the top-level IHostApplicationBuilder are somewhat unusual, so perhaps the library should also (or instead) consider providing an easier-to-use versions of:

extensions/src/Libraries/Microsoft.Extensions.AmbientMetadata.Application/ApplicationMetadataServiceCollectionExtensions.cs

Line 23 in 6eb7ad8

public static IServiceCollection AddApplicationMetadata(this IServiceCollection services, IConfigurationSection section)

So that we can simply use:

var builder = WebApplication.CreateBuilder(args);

builder.Configuration.AddApplicationMetadata();

builder.Services.AddApplicationMetadata();

Instead.

Currently, the second call is not possible as the caller is asked to provide the configuration section.

Risks

I believe zero, considering these would be additive APIs to the ones that exist today, so people can opt-in to the new HostApplicationBuilder-based configuration interface.