SDK: fix setting pipeline-wide artifact_location for ResourceOp and VolumeOp classes and add description field for create_experiment() function

[solovyevt]

Two things to update:

1. Fix setting artifact_location for Pipeline, it crashes due to non-existence of artifact_location field in ResourceOp and VolumeOp classes.
2. Add feature to add description to an experiment with dsl.

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This change is 

[k8s-ci-robot]

Hi @solovyevt. Thanks for your PR.

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[Ark-kun]

Thanks for your PR.
In future, please create separate PRs for separate issues so that they're easier to review and so that it's easier to understand the code annotations.
/lgtm

[Ark-kun]

/retest

[Ark-kun]

/approve

[k8s-ci-robot]

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