User Story:

As a user of the agent-based installer, I want to be able to:

• create agent ISO as well as PXE assets by providing the install-config.yaml

so that I can achieve

• create a cluster for external cloud provider platform type (OCI)

Acceptance Criteria:

Description of criteria:

• install-config.yaml accepts the new platform type "external"
• validate install-config so that platformName can only be set to `oci` when platform is external 
• agent-based installer validates the supported platforms
• agent ISO and PXE assets should be created successfully
• necessary unit tests and integration tests are added

(optional) Out of Scope:

Detail about what is specifically not being delivered in the story

Engineering Details:

• (optional) https://github/com/link.to.enhancement/
• (optional) https://issues.redhat.com/link.to.spike
• Engineering detail 1
• Engineering detail 2

This requires/does not require a design proposal.
This requires/does not require a feature gate.