Make helper pods spec, namespaces, and other features configurable.

[Tomcli]

This PR allows users to configure their helper pods specs and namespaces using the helm values.yml. The default namespace remains as default, but this will help us migrate to a dedicated namespaces in the future.

This PR also allows users to pick how to consume GPU resources via the values.yml, so they don't have to pull or build a different docker image for different environments.

All the major documentations are available at the developer-guide.md. This gives more options and flexibility for developers to try FfDL on different environments with different capability.

This closes #54, closes #55, and closes #56.

Signed-off-by: Tommy Li tommy.chaoping.li@ibm.com

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[Tomcli]

Moved to #110