Support multiple `PrivateLoadZone` objects

[yorugac]

Feature Description

As of now, k6-operator supports only one PrivateLoadZone at a time, or per installation. We'd like to extend support to multiple PrivateLoadZones.

Suggested Solution (optional)

The reconciler should move out polling logic into a new abstraction, with each PrivateLoadZone having its own goroutine to set up the poller, the factory and to handle the updates from the reconciler async.

The max number of PrivateLoadZones should be regulated by GCk6 and not by k6-operator.

Already existing or connected issues / PRs (optional)

No response

[yorugac]

Note: this work will not impact the load distribution of the test. IOW, even with multiple PLZs in the cluster, we'll support only 100% load or using 1 private load zone per test run.

[yorugac]

Closed in PR #558. Currently, the PLZs are distinguished by name only, namespace is unimportant. This is required to have backwards compatibility with the older PLZs. If identification scheme of a PLZ needs to change, it will be addressed with a separate issue and PR.

Since it's backwards compatible, there is no migration required: just an update of k6-operator to the latest (once it's released) should be sufficient to switch to the new setup. The start of the new version of app will read the existing PLZ in the system and continue to work as before, but now with potential to add more PLZs if you'd like.

The max number of PLZs is set by Grafana Cloud k6. By default, it is 5 per organization. If you need more, please reach out to customer support.