Add the possibility to disable `parallelPosting` for the `BlackBoxBoundedContext`

[dmytro-kashcheiev]

Currently it's impossible to disable parallelPosting for BlackBoxBoundedContext since it uses SystemSettings.defaults(). And by default for all environment except io.spine.base.Tests it will return SystemSettings with enabled parallel posting. As a result, you can't create your own test environments and use BlackBoxBoundedContext.

UPD. the issue has been addressed in 1.x-dev branch via #1495. We still need to address it in 2.x.

[armiol]

Here is how to disable the parallel posting for BlackBoxContext (at least, according to Spine 1.8.2 API):

        BoundedContextBuilder builder = newBuilder();
        builder.add(new MyAggregateRepository())
               .add(...);
        builder.systemSettings().disableParallelPosting();
        BlackBoxContext ctx = BlackBoxContext.from(builder);

@dmytro-kashcheiev please let me know if that works for you.

[armiol]

Addressed for v1 branch via #1495.

@dmytro-kashcheiev as of 1.9.0-SNAPSHOT.5 the code above works properly. This fix will be available as a part of 1.9.0 release.