feat(k6): add support for k8s loading/unloading of Seldon CRs

[lc525]

This adds initial support for k8s via the USE_KUBE_CONTROL_PLANE environment variable:

• models/pipelines/experiments in components/model.js are modified to also return CR yamls
• updates functions in components/utils.js (including setupBase(...) and teardownBase(...) to use xk6-kubernetes, when configured
• all scenarios already using setupBase(...) should work unchanged

Which issue(s) this PR fixes:

• INFRA-949 (internal issue) Extend existing k6 scenarios to use xk6-kubernetes

TODO

• [x] Test functionality in kind
• [x] Fix getting model/pipeline/experiment CRs back from k8s
• [x] Fix model/pipeline/experiment deletion
• [ ] Extend k6 scenarios not relying on setupBase(...) to use xk6-kubernetes