UI - Allow to define custom sort options for Test Env variables list

[jmorante-ks]

Is your feature request related to a problem? Please describe.
Currently the env variables is a map and not an ordered list, and Testkube UI is showing them always in alphabetical order.

This alphabetical order is not being useful for one customer, that wants to have them ordered in a custom way.

The customer needs to see always the most critical ones at the top of the list, so they need to have them in a custom order.

Describe the solution you'd like
The customer would like that Testkube saves the env variables order when you define them from the UI.

In other words, the test definition CRD should include not just the env variables, but also their order to be shown in the test settings screen.

It is also required to be possible to modify the order after the test creation, not just on initial creation. In other words order of variables should be editable at the settings screen of the test.