Document airgapped core provider installation

[alexander-demicev]

Cluster API publishes cluster-api-components.yaml in the release manifests, for example here https://github.com/kubernetes-sigs/cluster-api/releases/tag/v1.7.2, this file includes manifests for core CAPI and Kubeadm Bootstrap+CP providers. It might not be very clear to some users which manifests to use in air-gapped installaion, we need to document and provide an example of how to install all types of providers and which manifests to supply, core CAPI - core-components.yaml, infrastructure infrastructure-components.yaml, etc.