Simplify/Clarify Accelerators config

[wbuchwalter]

Accelerators configuration should be surfaced in chart's values.yaml, and examples should be provided for the different providers.

[jlewi]

In addition to letting users specify config directly, could we have an enum based on which we would select a default config suitable for a particular cloud so a user could do something like

helm install tf-job-operator-chart -n tf-job --wait --replace --set cloud=gke

or

helm install tf-job-operator-chart -n tf-job --wait --replace --set cloud=azure

The cloud value would be used to select from different config files provided as part of the chart.

For users would complete control they could do something like the following

helm install tf-job-operator-chart -n tf-job --wait --replace --set config-file=path/to/config.yaml