Add nodeSelectors and/or nodeAffinity/anti-affinity

[dgzlopes]

The Kubernetes scheduler can be constrained to place a pod on particular nodes using few different options. In your POD specification, there are many ways in which you declare a POD should be dedicated to specific nodes, one of them is nodeSelectors and another one is nodeAffinity/anti-affinity.

I would like to constrain where I can place k6 runners. This would open up a lot of fancy possibilities.

For example:

• Only use nodes from certain zones (and use Separate to spread the runners).
• Run my test on some type of instance (e.g. M4).
• Run my test on an isolated node pool of my cluster.