Description of problem:

An  Error 400 related to AWS VPC fetch failure has shown on cluster privacy > public subnet ID dropdown. The error hasn't given enough reason what was gone wrong and possible solution for the same cause and this fails for all the supported regions. We need to investigate 

1. If this is an expected error and what would be the cause of the same.
2. In case the above error is expected then would be good to improve this additional info about the cause and possible trouble shooting steps or direction to the user to solve this issue.

Steps to reproduce:

1. Launch OCM UI staging.
2. Open ROSA Cluster wizard.
3. Select the control plane as "Hosted" and proceed further.
4. Choose anyone of the manged polices listed on the ARN list and proceed next steps.
5. Under networking > configuration step, see the public subnet id field and associated error.
6. View the behavior.

Actual results:
The public subnet ID field has associated with inline error

Failed to fetch subnet IDs.
CLUSTERS-MGMT-400: An error occurred while retrieving AWS VPC list
Operation ID: 4c2fe079-db09-4b78-bb2c-b80dd4d5b33b 

The error doesn't give the reason for the failure and user has no clue what was gone wrong.

Expected results:
**

if  the above error is expected then would be good to improve this additional info about the cause and possible trouble shooting steps or direction to the user to solve this issue.