Create AWS EKS cluster from GitLab (Cluster Form Integration)

This MR is part of delivering #22392 (closed). It completes the implementation effort to deliver this feature 🎉. The changeset of this MR is focused on connecting the cluster configuration form with the BE APIs.

Screenshots

Implement a button to select a different AWS Role

Use GitLab APIs to populate cluster configuration dropdowns

Allow to select multiple subnets for a Kubernetes Cluster

Implement create cluster action

Testing

Before testing

• Enable create_eks_clusters feature flag
• In Admin -> Settings -> Integrations -> EKS integration, check the enabled box and enter the following into the form:

account_id: '123456789012' access_key_id: 'access_key_id' secret_access_key: 'secret_access_key'

To facilitate the QA process, we’ve set up an AWS service account for reviewers of the MR. The credentials will be provided via private channels. These credentials include the values expected in access_key_id, secret_access_key and the Role ARN.

How to test

• In the sidebar menu, select Operations -> Kubernetes
• Click "Add Kubernetes cluster" button.
• Click "Amazon EKS" button.
• You should see the Role ARN form. In the ARN field, introduce the ARN provided for QA purposes.

Documentation

We have documented this feature in a separate merge request !19667 (merged)

Conformity

• Changelog entry
• Documentation created/updated or follow-up review issue created
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team

Closes #22392 (closed)