PrivateLoadZone: make resources more flexible

[yorugac]

Feature Description

Currently, resources for PrivateLoadZone test runs are set only during creation of PLZ as part of its spec. To change them, one has to delete and re-create PrivateLoadZone object. This is a cumbersome way of dealing with resources and not well suited for the PLZ as a long-term CRD.

Suggested Solution (optional)

1. The simplest way to improve this approach is to make resources mutable: all PLZ test runs that are started after the edit of PLZ object are to use new values of resources.

2. A more complex option is to switch to a different way of resource definition in PLZ -- with a resource pool. In general, the test runs can be different: some of them are heavy and require a lot of resources, while other test runs are very small, e.g. with VU in {1, 10}, and could be executed with less resources. Having a resource pool available for PLZ test runs, GCk6 can then decide what kind of CPU and memory to designate for a specific test run.
   Switching to a resource pool would imply having a more complex logic in GCk6 but might result in a more efficient usage of computational resources overall.

This second option, with the pool, is currently more of an idea rather than a set course of action, and feedback on topic would be welcome.

Already existing or connected issues / PRs (optional)

The mutability of PLZ resources came up here:

• PrivateLoadZone resources should be immutable in CRD #382