This patch adds a holos component to deploy a SecretStore and
ExternalSecret in the default namespace to validate authentication with
Vault is configured correctly.
The default ksa is used to authenticate to vault.
Leaf directories can output different kinds of things:
1. Platform specification. A list of components to manage.
2. Kubernetes API Objects suitable for kubectl apply -f- and friends.
3. Helm values to provide to a helm chart to render API objects.
This patch adds an output schema and a kind discriminator so the holos
cli can figure out what type of output it's working with. This makes it
possible to have a single `holos build <directory>` command that does
the right thing.
