Create EKS cluster VPC and Subnet dropdown

This MR is part of delivering the feature #22392 (closed). It implements the dropdown to select an AWS VPC for a EKS Kubernetes cluster.

Feature screenshot

How to test this MR in your local environment

There are a few considerations to take into account when testing this merge request and others related to #22392 (closed).

• This merge request is part of a larger series of merge requests meant to deliver #22392 (closed). You can see the planned timeline in #22392 (comment 215156885).
• The backend for this feature is also a work in progress. The APIs the front-end consumes are not implemented yet. To keep making progress in the FE, we decided to include the AWS SDK for JavaScript as a temporary measure until back-end is ready. See gitlab-foss!32479 (merged) for more information.
• The two points above, make early merge requests like this one difficult to test in a local environment without considerable effort to setup requirements.
• Once back-end is ready and the FE/BE integration starts, this feature will be considerably easier to test.

To test this feature in your local environment, you have to:

• Enable the :create_eks_clusters feature flag.
• You’ll need an AWS account.
• In the Identity and Access Management (IAM), create a user with the following permissions: AmazonEC2ReadOnlyAccess and IAMReadOnlyAccess. Save somewhere the Access key ID and Secret Access Key.
• In the app/assets/javascripts/create_cluster/eks_cluster/index.js, paste the following code in the created entry point of the component:

// Initialize the Amazon Cognito credentials provider
    AWS.config = {
      region: 'us-east-1',
      accessKeyId: 'your access key',
      secretAccessKey: 'your secret'
    }

Also, import the following package import AWS from 'aws-sdk/global';