Handle etcd and kube-apiserver dependencies

User Story:

 I want hack/build.sh to embed the kube-apiserver and etcd dependencies in openshift-install without making external network calls so that ART/OSBS can build the installer with CAPI dependencies.

Acceptance Criteria:

Description of criteria:

• dependencies are not obtained over the internet
• gated by OPENSHIFT_INSTALL_CLUSTER_API env var
• should work when building for various architectures

(optional) Out of Scope:

Engineering Details:

• Currently the dependencies are obtained through the sync_envtest function in build-cluster-api.sh
• Cluster API provider dependencies are vendored and built here

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