[k8s] Handle invalid kubeconfig parsing

[kyuds]

Fixes #5989

Basically we will proceed by uploading the invalid kubeconfig, and throw the user a warning saying that things might not go as expected if they are indeed using k8s infra.

Tested (run the relevant ones):

• Code formatting: install pre-commit (auto-check on commit) or bash format.sh
• Any manual or new tests for this PR (please specify below)
• All smoke tests: /smoke-test (CI) or pytest tests/test_smoke.py (local)
• Relevant individual tests: /smoke-test -k test_name (CI) or pytest tests/test_smoke.py::test_name (local)
• Backward compatibility: /quicktest-core (CI) or pytest tests/smoke_tests/test_backward_compat.py (local)

[kyuds]

/smoke-test --kubernetes

[romilbhardwaj]

Thanks @kyuds!