Extract task execution attributes into an inlined struct

[olim7t]

What is missing?

In k8ssandra/k8ssandra-operator#739 we will introduce a K8ssandraTask resource, that triggers a CassandraTask for each datacenter in the cluster:

apiVersion: control.k8ssandra.io/v1alpha1
kind: K8ssandraClusterTask
metadata:
  name: upgradesstables
spec:
  cluster:
    name: cluster1
  datacenters:
    - dc3
    - dc1
  spec:
    jobs:
      - name: upgradesstables-dc1
        command: upgradesstables

The spec part is almost identical to CassandraTask, except that it won't have a datacenter field. It would be nice to have a struct that we can reuse, instead of duplicating all the required fields.

Why do we need it?

Code reuse, maintainability.

Environment

Any.

• Cass Operator version: > 1.13.1

Anything else we need to know?: