move python modules out of bzl file

[cristifalcas]

I moved only the pip packages in WORKSPACE.

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[cristifalcas]

/assign @nlopezgi

[cristifalcas]

@googlebot I signed it!

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[nlopezgi]

/gcbrun

[nlopezgi]

/gcbrun

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: cristifalcas, nlopezgi

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