Don't set empty CPU limits to CPU requests

[flixr]

Currently a (container) task with only CPU requests but no limits set, still gets limits applied:

from flytekit import ContainerTask, kwtypes, workflow, Resources

hello_task = ContainerTask(
    name="hello",
    image="ubuntu:20.04",
    requests=Resources(cpu="2", mem="1Gi"),
    limits=Resources(mem="2Gi"),
    command=["echo", "hello"]
)

Running this task results in a pod with cpu limit also set to 2 (same as request), but there should be no cpu limit.

In many cases setting CPU limits (not requests) results in unused CPU due to throttling, see also
https://home.robusta.dev/blog/stop-using-cpu-limits.

So I propose to only copy the requests to limits as a whole if limits are completely unset instead of filling missing limits with the respective requests values.

Originally I created this as a bug: #3574

[cosmicBboy]

hi @flixr this is a bug we want to address, but it doesn't fit the RFC criterion of being a significant change, gonna close this discussion and please feel free to contribute a PR, or ping the flyte snack contribute channel if you want to raise awareness of this issue to the community

[cosmicBboy]

Closing this discussion, see #3574