Add AWS IAM Role and Key Pair fields to EKS Cluster form

This MR is part of delivering the feature #22392 (closed). It implements the dropdown to select an AWS IAM Role and Key Pair for an EKS Kubernetes cluster.

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';