Ensure that validating webhooks for Machine API will reject mismatched platform types

User Story

As a user I would like to ensure that I don't create Machines or MachineSets that have the incorrect provider spec for the platform. Having a check in the validating webhooks would ensure that I do not create Machine records which are difficult to remove.

Background

In a recent discussion from internal Red Hat slack, a customer has created a Machine record for AWS that contains a vSphere provider spec. This has resulted in a Machine object which will not delete cleanly as the webhooks will not validate it (since the provider spec contains the wrong fields), and removing the finalizer does not help this situation.

Discussion from slack (this will not work for non-Red Hatters): https://coreos.slack.com/archives/CBZHF4DHC/p1642711385068300

Steps

• Ensure that the validating webhooks will check the provider spec to ensure that it is the proper type for the platform.

Stakeholders

• OpenShift SRE

Definition of Done

• Validating webhooks don't allow creation of records with a mismatched ProviderSpec

• Docs

• This should not require a docs update

• Testing

• Unit tests should be created to ensure this is rejected