Description of problem:

In the ROSA or OSD cluster wizard, show the instance types in the machine pool step based on the region selection done by the user. Currently it doesn't work in the same way. For example,

User has chosen the region us-east-2 and the instance type as Hpc6a.48xlarge.

But the cluster initiation has failed in the UI indicated below error.

It would be better to avoid such confusions by restricting the user to select non supported instances from the selected region.

How reproducible:

 Always

Steps to Reproduce:

1. Launch OCM in staging.
2. Start OSD/ROSA cluster creation wizard.
3. In Cluster settings >  Cluster details > region > us-east-2.
4. Move to the next step, select the Compute node instance type as Hpc6a.48xlarge.
5. Reach to the "review and create" page.
6. Click on the "create cluster" and view the behavior.

Actual results:

Cluster installation reported an error stating that the selected instance type was not supported  on the availability zone in the selected region.
CLUSTERS-MGMT-400: Instance type 'hpc6a.48xlarge' is not supported on availability zone 'us-east-2a'Operation ID: d9f3192f-2819-4df1-b32d-5e93d3139265

Expected results:

Users should restrict selecting the non supported instance type for the selected region from cluster wizard i.e. only supported instance should list for the selected region in cluster wizard.
This will avoid these errors and confusions.