Describe the bug

Custom WireMock images that include their own mappings like from the guide can not be used in WireMockContainerBuilder.WithImage() leading to a InvalidOperationException on Build() because _imageOS is never set.

Expected behavior:

var container = new WireMockContainerBuilder()
            .WithLinuxImage()
            .WithImage("custom-wiremock:latest")
            .WithAutoRemove(true)
            .WithCleanUp(true)
            .Build();

await container.StartAsync().ConfigureAwait(false);
var client = container.CreateClient();
// Start requesting the built-in mappings

I expect with the above code to work an not throw an exception. However after WithLinuxImage() _imageOS is still set to null because the builder objects gets recreated from scratch with only the docker config remaining.