feat(microservices): add status, unwrap, on, and other features

[kamilmysliwiec]

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/nestjs/nest/blob/master/CONTRIBUTING.md
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Other... Please describe:

What is the current behavior?

Issue Number: #14044 #11913 #14140

What is the new behavior?

Improvements: graceful reconnection for all transporters, exposed API to listen to internal events, ability to unwrap the client proxy and retrieve the underlying client/server reference, exposed status stream to subscribe to recent client status changes.

Use-cases:

1. React to status changes from server instances or client proxies:

const serviceRef = app.connectMicroservice({
  transport: Transport.NATS,
  options: {},
});

serviceRef.status.subscribe(status => {
  console.log('Status:', status);
});

Client:

this.clientProxy.status.subscribe(status => {
  console.log('Status:', status);
});

2. Listen to underlying, transport-specific events:

const serviceRef = app.connectMicroservice({
  transport: Transport.NATS,
  options: {},
});

serviceRef.on<NatsEvents>('disconnect', () => {
  console.log('Client disconnected');
});

Client:

// inject passing the type argument specific to the transport strategy you use
constructor(
  @Inject(MATH_SERVICE) private readonly client: ClientProxy<NatsEvents>,
) {}

// use the "on" method somewhere else
this.client.on('disconnect', () => console.log('Disconnected'));

3. Access the underlying server/client instance:

import { NatsConnection } from 'nats';

// in the bootstrap function
const serviceRef = app.connectMicroservice({
  transport: Transport.NATS,
  options: {},
});

const connection = serviceRef.unwrap<NatsConnection>();
console.log(connection.info);

Same API for the ClientProxy class

Does this PR introduce a breaking change?

• Yes
• No

Other information