add runtimeclassname for both ray head and worker pod

[xinchi-he]

This PR adds runtimeClassName specification at the chart level. (e.g. runtimeClassName: nvidia) The example use case here is to inject GPU access (drivers, libraries, and devices) to either ray head or worker pods.

Unit tests are also added.

### Chart [ ray-cluster ] .

 PASS  Test RayCluster  tests/raycluster_test.yaml

Charts:      1 passed, 1 total
Test Suites: 1 passed, 1 total
Tests:       99 passed, 99 total
Snapshot:    0 passed, 0 total
Time:        166.47875ms

[rubenjacob]

Adding this field would help us greatly, as it seems to be the only way at the moment to reliably get pods to use the nvidia RuntimeClass. 👍