Allow RequestLoggingOptions configuration outside of Configure(IApplicationBuilder)

[skomis-mm]

It is a common pattern to configure middleware options outside of Configure(IApplicationBuilder). It could be a different module, for example. It also integrates with Microsoft.Extensions.Options. This PR will allow such configuration:

public void ConfigureServices(IServiceCollection services)
{
    services.Configure<RequestLoggingOptions>(Configuration.GetSection("Serilog")); // get MessageTemplate from appsettings.json
    services.PostConfigure<RequestLoggingOptions>(options =>
    {
        options.EnrichDiagnosticContext = (diagnosticContext, httpContext) =>
        {
            diagnosticContext.Set("RemoteIpAddress", httpContext.Connection.RemoteIpAddress.MapToIPv4());
        };
    });
}

public void Configure(IApplicationBuilder app)
{
    // ..
    app.UseSerilogRequestLogging();
    app.UseRouting();
    // ...
}

[nblumhardt]

Looks great! Ready to merge?

[skomis-mm]

@nblumhardt , yes, its pretty complete

[sungam3r]

)

[sungam3r]

This parameter seems (a bit) redundant now.

[mkgn]

Can RequestLoggingOptions() be enabled/disabled via appSettings.json file under Serilog settings?