This feature requires that the ROSA and OSD provisioning wizards have a new option where the customer can 

1. ignore infra-node instance-type selection and get m5 series instead of r5 series, in case r5 is not available in their chosen region
2. have the option to specify m5 series instead of r5 series for their cluster's infra nodes
3. There should be a short text box explaining this with a link to the docs coverage

This probably belongs in the wizard below the existing (step 2, default machine pool) with the title "Infrastructure nodes" and the subtitle "Alternative Infrastructure Node instance type".

If it is detected that the user does not have access to r5-series in their chosen region and must use m5 instead, then the field will be auto-selected and greyed out.