feat: allow for microservice options to come from the di container

Microservices are now able to be created by getting their options
from within the DI container itself. This has been a long requested
feature of developers and I finally had some time to work through how
we could possibly let this happen.

integration/microservices/e2e/sum-rpc-async.spec.ts

@@ -0,0 +1,98 @@
+import {
+  Controller,
+  INestMicroservice,
+  Injectable,
+  Module,
+} from '@nestjs/common';
+import {
+  AsyncOptions,
+  ClientTCP,
+  ClientsModule,
+  MessagePattern,
+  MicroserviceOptions,
+  Payload,
+  TcpClientOptions,
+  Transport,
+} from '@nestjs/microservices';
+import { expect } from 'chai';
+import { NestFactory } from '@nestjs/core';
+
+let port: number;
+
+do {
+  port = Math.round(Math.random() * 10000);
+} while (port < 1000);
+
+@Injectable()
+class RpcOptionsProvider {
+  getOptions(): TcpClientOptions {
+    return {
+      transport: Transport.TCP,
+      options: {
+        port,
+        host: '0.0.0.0',
+      },
+    };
+  }
+}
+
+@Controller()
+class RpcController {
+  @MessagePattern({ cmd: 'sum' })
+  sumPayload(@Payload() payload: number[]) {
+    return payload.reduce((a, b) => a + b, 0);
+  }
+}
+
+@Module({
+  imports: [
+    ClientsModule.register([
+      {
+        name: 'RPC_CLIENT',
+        transport: Transport.TCP,
+        options: {
+          port,
+          host: '0.0.0.0',
+        },
+      },
+    ]),
+  ],
+  controllers: [RpcController],
+  providers: [RpcOptionsProvider],
+})
+class RpcModule {}
+
+describe('RPC Async transport', () => {
+  let app: INestMicroservice;
+  let client: ClientTCP;
+
+  beforeEach(async () => {
+    app = await NestFactory.createMicroservice<
+      AsyncOptions<MicroserviceOptions>
+    >(RpcModule, {
+      logger: false,
+      inject: [RpcOptionsProvider],
+      useFactory: (optionsProvider: RpcOptionsProvider) =>
+        optionsProvider.getOptions(),
+    });
+
+    await app.listen();
+    client = app.get('RPC_CLIENT', { strict: false });
+  });
+
+  it(`/POST`, done => {
+    let retData = 0;
+    client.send({ cmd: 'sum' }, [1, 2, 3, 4, 5]).subscribe({
+      next: val => (retData += val),
+      error: done,
+      complete: () => {
+        expect(retData).to.eq(15);
+        done();
+      },
+    });
+  });
+
+  afterEach(async () => {
+    await app.close();
+  });
+});