feat(sdk/backend): Add support for placeholders in resource limits

[rimolive]

The API introduced new fields prefixed with Resource (e.g. ResourceCpuLimit) to replace the old fields without the prefix. The Driver hadn't been updated to honor those fields but the SDK started using them which led to unexpected behavior.

The Driver now honors both fields but prioritizes the new fields. The SDK now only sets the new fields.

The outcome is that resource limits/requests can now use input parameters.

Note that pipeline_spec_builder.py was doing some validation on the limits/requests being set, but that's already handled in the user facing method (e.g. set_cpu_limit).

Resolves:
kubeflow#11500

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