Async Init

[mjarmoc]

This PR changes the way RMQ Service is provided.

Problem:

It is very painfull during tests execution:

app = moduleFixture.createNestApplication();
await app.init();
NEST APP IS LIVE NOW, BUT IT IS NOT READY TO OPERATE, SINCE CONNECTION TO RABBIT MAY NOT BE ESTABLISHED YET

Plans:

I would like to prepare separate Connection class and factory, similar as it is done in @nestjs/mognoose package. For now, I am proposing smaller and faster solution.

Before:

The init() method establishing the connection is called inside the constructor in async way. The RMQService may be provided, but not ready to operate.

[Nest] 26975   - 04/16/2020, 10:42:51 PM   [NestFactory] Starting Nest application...
[4/16/2020] [10:42:51 PM] › …  watching  Connecting to RMQ
[Nest] 26975   - 04/16/2020, 10:42:51 PM   [InstanceLoader] RMQModule dependencies initialized +30ms
[Nest] 26975   - 04/16/2020, 10:42:51 PM   [InstanceLoader] AppModule dependencies initialized +0ms
[Nest] 26975   - 04/16/2020, 10:42:51 PM   [RoutesResolver] AppController {}: +6ms
[Nest] 26975   - 04/16/2020, 10:42:51 PM   [RouterExplorer] Mapped {, GET} route +3ms
[Nest] 26975   - 04/16/2020, 10:42:51 PM   [NestApplication] Nest application successfully started +2ms
**| NEST APP IS LIVE HERE BUT NOT READY !! |**
[4/16/2020] [10:42:51 PM] › ✔  success   Successfully connected to RMQ

After:

The init method is called sync inside the provider factory. When the connection is sucessfuly established, the provider is resolved.

[Nest] 2818   - 04/17/2020, 8:20:48 AM   [NestFactory] Starting Nest application...
[4/17/2020] [8:20:48 AM] › …  watching  Connecting to RMQ
[Nest] 2818   - 04/17/2020, 8:20:48 AM   [InstanceLoader] AppModule dependencies initialized +62ms
[4/17/2020] [8:20:48 AM] › ✔  success   Successfully connected to RMQ
[Nest] 2818   - 04/17/2020, 8:20:48 AM   [InstanceLoader] RMQModule dependencies initialized +85ms
[Nest] 2818   - 04/17/2020, 8:20:48 AM   [NestApplication] Nest application successfully started +6ms
**| NEST APP IS LIVE AND READY !! |**

[AlariCode]

@mjarmoc Thx! I will review it in several days.

[AlariCode]

@mjarmoc added your code to master branch and published in nestjs-rmq@1.7.0 (faster then merging your PR, because of code conflicts). Thanks for contributing!