Add `envFrom` in dask/dask workers deployment

[RRRajput]

Currently there is no envFrom option to provide the environment variables from a ConfigMap or Secret to the dask workers. All the environment variables must be defined one by one which can get quite cumbersome.

I can take this issue up myself if needed.

[jacobtomlinson]

@RRRajput that sounds great! Feel free to ping me on the PR for review.