Make opencloud service HA

[butonic]

Not all services of the opencloud pod can be scaled horizontally:

• the idm uses boltdb: introduce internal openldap #96
• the built in nats server does not support cluster mode: support external nats #92
• the search service is based on bleve, which uses boltdb
• the PV used by storage-users and storage-system must support ReadWriteMany

I pulled out idm and nats, but the search service needs to be put in a dedicated pod, still.

For the storage services we should check the PV is configured to be ReadWriteMany when replicas is greater than 1.

Finally, opencloud currently uses a service registry based on NATS. For HA we want to prevent requests to be routed between the opencloud pods. To do this, we can skip the service registry and use unix sockets for pod internal communication. This needs more investigation, maybe setting the service endoints to 127.0.0.1 works, but the service registry might ovveride it with the external ip.