feat: add close() API

[schmidt-sebastian]

Fixes: #68

[merlinnot]

It looks like we should return a Promise here, so that users can await it?

Suggested change

	close(): void {
	close(): Promise<void> {

[schmidt-sebastian]

The method we are invoking is synchronous: https://github.com/grpc/grpc-node/blob/master/packages/grpc-js/src/client.ts#L90

[merlinnot]

Yes, but this._{{ service.name.toCamelCase() }}Stub is a Promise and we use it here.

[schmidt-sebastian]

Hm, I was hoping close() could be synchronous, but you are right. I updated the PR.

[alexander-fenster]

Unfortunately, due to the asynchronous nature of the constructor (it fires some promises to initialize the stubs), all member functions working with a stub must be asynchronous (must wait on the stubs to be complete).

[alexander-fenster]

@schmidt-sebastian Can you run npm run baseline to update the generated baselines and add that changes to this PR?

Upd: oops, sorry, the test failure is not related to baselines. I'll take a look what's wrong there.

[alexander-fenster]

@schmidt-sebastian Seems like the generated code cannot compile:

If you run npm test, the .test-showcase-out will contain a generated client library for showcase API that you should be able to compile.

[schmidt-sebastian]

I just learned a lot about this tooling :) The generated code should compile now, but it doesn't since we need to export the APICallback type. I'll create a PR for that in google-gax.

[alexander-fenster]

looks like the condition must be reversed