Snippeet for injecting reloadable strongly typed configuration into your asp.net core Web API

Injecting AspNet.Core Configuration

Let's say that your appsettings.{envinronment}.json looks like this.

```
{
  "DatabaseConfiguration": {
    "apiDb": "Server={localhost};Initial Catalog={database};User ID={userName};Password={password};",
    "api2Db": "Server={localhost};Initial Catalog={database};User ID={userName};Password={password};"
  },
}
```

To achive a strongly typed injectable configuration you will need this.

1. Create a POCO class that maps to your appsettings (desired section, it doesn't have to be the whole file)
```
namespace CoreStarter.Api.Configuration
{
    public class ConnectionStrings
    {
        public string ApiDb { get; set; }

        public string Api2Db { get; set; }
    }
}
```

2. Startup configuration 
```
public IServiceProvider ConfigureServices(IServiceCollection services)
{
    IConfigurationRoot configuration =
        new ConfigurationBuilder()
            .SetBasePath(_env.ContentRootPath)
            .AddJsonFile("appsettings.json", optional: false, reloadOnChange: true)
            .AddJsonFile($"appsettings.{_env.EnvironmentName}.json", optional: true, reloadOnChange: true)
            .AddEnvironmentVariables()
            .Build();

    services.Configure<ConnectionStrings>(configuration.GetSection("ConnectionStrings"));
}
```

3. Inject it
```
public FooController(IOptionsSnapshot<ConnectionStrings> connectionStrings, IFooService service, ILogger<FooController> logger)
{
    _connectionStrings = connectionStrings.Value ?? throw new ArgumentNullException(nameof(connectionStrings));
    _service = service ?? throw new ArgumentNullException(nameof(service));
    _logger = logger ?? throw new ArgumentNullException(nameof(logger));
}
```