Configurable operator CLI tool to generate yaml files

[sebgl]

Configurable operator meta issue and design proposal.

As described in the design proposal, we need some tooling to generate yaml specifications of the operator(s) to deploy, including RBAC permissions.

An example (just a draft, can be implemented differently):

# cli sample usage (exact specification TBD)
> ./elastic-operator generate --config=operators.yaml
# generates one or multiple yaml files ready-to-deploy, including Deployment, ServiceAccount, (Cluster)Roles, (Cluster)RoleBindings, etc.

# sample configuration (exact specification TBD)
operators:
    # manage clusters in namespace "team-A-production"
    - image: docker.elastic.co/k8s-operators:1.0
      roles: ["elasticsearch", "kibana"]
      managedNamespaces: ["team-A-production"]
      namespace: "team-A-production"
    # manage clusters in namespace "team-A-development"
    - image: docker.elastic.co/k8s-operators:1.1-alpha1
      roles: ["elasticsearch", "kibana"]
      managedNamespaces: ["team-A-development"]
      namespace: "team-A-development"
    # manage enterprise licenses in all namespaces
    - image: docker.elastic.co/k8s-operators:1.0
      roles: ["licensing"]
      clusterWide: true
      namespace: "elastic-system"
    # manage CCS/CCR in namespaces "team-A-production" and "team-B-production"
    - image: docker.elastic.co/k8s-operators:1.0
      roles: ["cross-cluster"]
      managedNamespaces: ["team-A-production", "team-B-production"]
      namespace: "elastic-system"

[pebrc]

Closing this in favour of #2406