Avoid naming overflow in k8s

[fpacifici]

Cap the size of the pipeline-pp label in the pipeline step macro.
pipeline-app is the whole python package so it can be logner than
63 characters, which is the maximum allowed by k8s.

I would like to remove this label entirely. I doubt it would actually
be useful, but selector labels require the deployment to be recreated
to make changes, so we only cap it

[cursor]

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