Allow sets on Metadata

[AlexejPenner]

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System Information

Though set is listed as allowed in MetadataType it can't be used, cause there is a json.dumps call under the hood, which fails for obvious reasons on sets.

What happened?

Sets dont work in MetadataType

Reproduction steps

just log some set as run metadata.

Relevant log output

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[AlexejPenner]

This is linked to https://zenmlteam.slack.com/lists/T02FAMHGZL4/F08MTECN9CK?record_id=Rec09VA03NULE