Remove default EKS Regions in create form

What does this MR do?

When a user wants to create a new EKS cluster, we default their region to us-east-2.

This is causing some customers to view the wrong list of regions. See issue: #216974 (closed)

There is also an issue of government regions being block, which may be the same issue: #231525 (closed)

Proposed solution: remove the dropdown and automatic assignment of regions. Instead, ask the customer to enter their regions manually.

This will not solve Connectivity or Permission Issues, but it will prevent GitLab from only loading us-east-2 regions.

Screenshots

form

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• 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
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

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