By default, CloudNativePG creates three Kubernetes services for
applications to access the cluster via the network:

- One pointing to the primary for read/write operations.
- One pointing to replicas for read-only queries.
- A generic one pointing to any instance for read operations.

This patch introduces managed services via the `managed.services`
stanza, allowing you to:

- Disable the read-only and read services via configuration.
- Leverage the service template capability to create custom service
   resources, including load balancers, to access PostgreSQL outside
   Kubernetes (this is particularly useful for DBaaS purposes).

Closes #4339

Signed-off-by: Armando Ruocco <armando.ruocco@enterprisedb.com>
Signed-off-by: Gabriele Bartolini <gabriele.bartolini@enterprisedb.com>
Signed-off-by: Tao Li <tao.li@enterprisedb.com>
Signed-off-by: Marco Nenciarini <marco.nenciarini@enterprisedb.com>
Co-authored-by: Gabriele Bartolini <gabriele.bartolini@enterprisedb.com>
Co-authored-by: Tao Li <tao.li@enterprisedb.com>
Co-authored-by: Marco Nenciarini <marco.nenciarini@enterprisedb.com>