Create `ClusterSecretStore` that can be used for bootstrapping the required secrets

[lentidas]

Quick notes:

• the user needs to be able to enable or disable the deployment of the ClusterSecretStore;
• we need to find a way to let the ClusterSecretStore access the secrets backend (on EKS and SKS that could be easy through an annotation, on other providers we might need to deploy a Kubernetes secret somehow);