Add PrivateLoadZone CRD

[yorugac]

Define and add PrivateLoadZone CRD following this approximate spec:

apiVersion: k6.io/v1alpha1
kind: PrivateLoadZone
metadata:
  name: amazing-plz
spec:
  token: cloud-token # mandatory
  resources: # mandatory
    cpu: ...
    memory: ...
  serviceAccountName: ... # or default
  nodeSelector: # or nil
    foo: bar

Subtasks:

• Support loading token with the name in addition to labels.
• Add PLZRegistered and CloudPLZTestRun conditions.
• Once registered and if polling is not running, start the polling.
• Polling test runs, sending to the channel. Create K6 resource for each test run.
• On deletion of PLZ, call deregister.
• Pass additional fields of PLZ CRD to K6 CRD.

[yorugac]

Most of the points were implemented in PR #238 except for:

On deletion of PLZ, call deregister.

Working deregistration is part of PR #239