User's 'Add Cluster' for EKS should include details of ECR in same region

[concurrent-ai]

We have the ability for a user to 'Add Cluster' by pressing the Gear icon in the MLflow ui. Right now, we prompt for EKS Region, EKS ROle and EKS External ID. We need to prompt for ECR details as well. Here is what I have in mind.

1. Cluster Name
2. Namespace
3. Type - EKS or GKE permitted. Let's say user chooses EKS
4. EKS and ECR Region
5. EKS Role
6. EKS External ID
7. ECR Type (allowed values are private and public)
8. Use EKS Role and External ID for ECR (if user unchecks this checkbox, two new boxes appear below)
9. ECR Role
10. ECR External ID

The REST API has been enhanced to take new parameters:

• ecr_region
• ecr_type
• ecr_role
• ecr_role_ext
  These must always be filled in if cluster_type == 'EKS'