Explore - Rewrite Fluent API

[adammorr]

@slang25 first pass of exploring/rewriting the fluent API and splitting out/changing the underlying bus implementations

// Configure bus (regions, dependencies etc.)
var configuredBus = new BusBuilder().UsingAws(cfg =>
{
    cfg.UseRegions("eu-west-1", "eu-central-1");
    cfg.ConfigureDependencies(dep =>
    {
        dep.MessageMonitor = new NullOpMessageMonitor();
    });
});

// Publisher
var publisher = await configuredBus.CreatePublishers()
    .AddTopicPublisher<MessageOne>(cfg =>
    {
        cfg.TopicNameOverride = "override-topic-name";
        cfg.AdditionalSubscribers = new[] {"123", "456", "789"};
    })
    .AddQueuePublisher<MessageTwo>(cfg =>
    {
        cfg.QueueNameOverride = "override-queue-name";
        cfg.DeliveryDelaySeconds = 10;
        cfg.ErrorQueueOptOut = true;
        cfg.ErrorQueueRetentionPeriodSeconds = 300;
        cfg.MessageRetentionSeconds = 30;
        cfg.RetryCountBeforeSendingToErrorQueue = 8;
        cfg.VisibilityTimeoutSeconds = 30;
    })
    .BuildAsync();

await publisher.PublishAsync(new MessageOne());

// Subscriber
var subscriber = await configuredBus.CreateSubscribers()
    .AddTopicSubscriber(cfg =>
    {
        cfg.TopicNameOverride = "override-topic-name";
    })
    .WithHandler(new MessageOneHandler())
    .AddQueueSubscriber(cfg =>
    {
        cfg.QueueNameOverride = "override-queue-name";
    })
    .WithHandler(new MessageTwoHandler())
    .BuildAsync();

subscriber.StartListening();
subscriber.StopListening();

[jaimalchohan]

LGTM 👍

[gerektoolhy]

@stuart-lang

Few things come to my mind. Not necessarily they are related to this PR:
a) AddQueuePublisher and AddTopicPublisher to support Type param as the message type. Easy and not intrusive change.
b) Is it possible to configure globaly bus defaults? E.g. Default retention period. Is this just as easy as modifying the variable in the constants file? (sorry, do not remember the name of the file, but i've seen there is global defaults somewhere)
c) Current issue we have is that it takes somewhat longish to initialize a bus, as each topic and subscriber is initialized. This can be alleviated to some extent by not re-checking if the same queue/topic exists multiple times. Some sort of caching layer during startup would help here. Have not seen existing code, so not sure if this is already done or not.
d) AddQueueSubscriber and accompanying AddTopicSubscriber there's something with these that does not feel right. I know this is more or less of what we have currently. I'll need to download and play around with the fluent interface to come up with something else. Can you ping me please.

@stuart-lang Which branch contains the latest code, i'd like to see if i can come up with some suggestions/improvements to the fluent API.

[AnthonySteele]

Resubmit as a "ready to merge" PR when it's ready to go.
Maybe after v6.0 is out?