Set indentation to zero when including file fragments

[octonato]

As discussed here:
https://github.com/akka/akka-platform-guide/pull/322#discussion_r508310150

Ideally we could solve that using styling.

It can be a challenge when including different fragments by toggling the same tag.

For instance, this:

// tag::SendOrderProjection[]
import shopping.order.proto.ShoppingOrderService;
import shopping.order.proto.ShoppingOrderServiceClient;
import akka.grpc.GrpcClientSettings;
// end::SendOrderProjection[]

public class Main extends AbstractBehavior<Void> {

    public Main(ActorContext<Void> context) {
        // tag::SendOrderProjection[]
        ShoppingOrderService orderService = orderServiceClient(system);
        SendOrderProjection.init(system, orderService);
        // end::SendOrderProjection[]
    }

    // can be overridden in tests
    // tag::SendOrderProjection[]
    protected ShoppingOrderService orderServiceClient(ActorSystem<?> system) {
        GrpcClientSettings orderServiceClientSettings =
                GrpcClientSettings
                        .connectToServiceAt(
                                system.settings().config().getString("shopping-order-service.host"),
                                system.settings().config().getInt("shopping-order-service.port"),
                                system)
                .withTls(false);

        return ShoppingOrderServiceClient.create(orderServiceClientSettings, system);
    }
    // end::SendOrderProjection[]
}

will show as:

import shopping.order.proto.ShoppingOrderService;
import shopping.order.proto.ShoppingOrderServiceClient;
import akka.grpc.GrpcClientSettings;
        ShoppingOrderService orderService = orderServiceClient(system);
        SendOrderProjection.init(system, orderService);
    protected ShoppingOrderService orderServiceClient(ActorSystem<?> system) {
        GrpcClientSettings orderServiceClientSettings =
                GrpcClientSettings
                        .connectToServiceAt(
                                system.settings().config().getString("shopping-order-service.host"),
                                system.settings().config().getInt("shopping-order-service.port"),
                                system)
                .withTls(false);

        return ShoppingOrderServiceClient.create(orderServiceClientSettings, system);
    }

while we probably want it to be:

import shopping.order.proto.ShoppingOrderService;
import shopping.order.proto.ShoppingOrderServiceClient;
import akka.grpc.GrpcClientSettings;

ShoppingOrderService orderService = orderServiceClient(system);
SendOrderProjection.init(system, orderService);

protected ShoppingOrderService orderServiceClient(ActorSystem<?> system) {
    GrpcClientSettings orderServiceClientSettings =
        GrpcClientSettings
            .connectToServiceAt(
                system.settings().config().getString("shopping-order-service.host"),
                system.settings().config().getInt("shopping-order-service.port"),
                system)
            .withTls(false);

	return ShoppingOrderServiceClient.create(orderServiceClientSettings, system);
}

Most probably we can't solve this with styling though.

We will need to have different tags: tag::SendOrderProjection-part1[], tag::SendOrderProjection-part2[], tag::SendOrderProjection-part3[], etc.