docs(samples): add usage samples to show handling of LRO response Operation

[Shabirmean]

Fixes #415

Description

• For a detailed description read internal ref b/189985582
• The Kubernetes engine API protos were written before the API Improvement Proposal (AIP-151)
• AIP-151 suggests to annotate API calls that takes a long time to complete with a certain annotation. This will enable the auto-generator (that generates our client libraries) to wrap the response an object of type google.longrunning.Operation in a language native (Python Future or Nodejs Promise) async construct.
• However, since AIP-151 came long after the container.v1 API protos were written, the container API protos don't have the necessary annotation as guided in AIP-151
• As a result the auto generated container client libraries do not return the very useful google.longrunning.Operation object, instead they return google.container.v1.Operation
• This object does not have the necessary built-ins to easily verify if the operation has completed.
• This this PR adds a few samples to show to customers how they can use this Operation object to validate if their operation has successfully completed using polling with backoff on the getOperation() API

Changes

• Added 2 samples (create_cluster & delete_cluster) to showcase usage of the library and to show how to handle responses of type google.container.v1.Operation
• Upon creation we use a fibonacci backoff to retry until the operation is complete
• I have also added test cases for the added samples

Testing

• Create a project
• Enable the container (GKE) API
• Create a service account with permissions to create/delete clusters (can use Owner)
• Download a key for the created service account

export GOOGLE_APPLICATION_CREDENTIALS="<PATH_TO_KEY>"
gcloud config set project <GCP_PROJECT>

cd <repo_path>
git checkout lro-fix

node samples/create_cluster.js --zone=us-central1-b --name=gke10
node samples/delete_cluster.js --zone=us-central1-b --name=gke10

npm run samples-test

[Shabirmean]

@sofisl - Please TAL and let me know if it's good!

[Shabirmean]

This autogenerated usage is not correct. Im not sure how I can change this. In any case it doesn't break anything. The user will get a message indicating required args on first run

[generated-files-bot]

Warning: This pull request is touching the following templated files:

• README.md - README.md is managed by synthtool. However, a partials file can be used to update the README, e.g.: https://github.com/googleapis/nodejs-storage/blob/main/.readme-partials.yaml
• samples/README.md - samples/README.md is managed by synthtool. However, a partials file can be used to update the README, e.g.: https://github.com/googleapis/nodejs-storage/blob/main/.readme-partials.yaml

[snippet-bot]

Here is the summary of changes.

You are about to add 3 region tags.

• samples/create_cluster.js:30, tag gke_create_cluster
• samples/delete_cluster.js:28, tag gke_delete_cluster
• samples/quickstart.js:17, tag gke_list_cluster

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[NimJay]

Thanks for the very detailed pull-request description, Shabir. 👏

I have yet to provide more rigorous feedback and test the two scripts.
I'll likely be making some tweaks to this pull-request some time this week.

In the meantime, I realized that one of the tests is failing on Kokoro.
I believe it's because Node.js 12 doesn't support Crypto.randomUUID().
Judging from this article and this StackOverflow post, we may need to:

npm install uuid

If we could somehow use Node.js 14.17 or higher, we could use crypto.randomUUID natively. But I assume a Node upgrade is outside the scope of this PR.

[sofisl]

Since all the create and delete files are so similar, all of my comments for create apply to delete as well.