Support running CouchbaseBackup and CouchbaseBackupRestore jobs on particular nodes

As a system administrator, it would be useful to be able to run backup and restore jobs on particular Kubernetes nodes. For example, I may need those jobs to run on specialized hardware, have access to particular virtual resources, not consume capacity in a cluster's "default" node pool, or satisfy logical technical requirements.

Ideally, implementing this improvement would involve adding support for the following Kubernetes features to the CouchbaseBackup and CouchbaseBackupRestore custom resources:

• node selector and/or node affinity
• [tolerations|https://kubernetes.io/docs/concepts/scheduling-eviction/taint-and-toleration/]