Enable SI units conversion on dataset update

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Issue Name

Enable SI units conversion on dataset update

Summary

SI units conversion seems to be enabled on datasets creation only. Extend the logic to work on dataset update

Steps to Reproduce

Update a datasets adding scientificMetadata: {something: {value:10, unit; cm}}. No SI extra pair is stored alongside of value and unit

Current Behaviour

SI are not added

Expected Behaviour

SI should be added.

Extra Details

Here you should include details about the system (if it is unique) and possible information about a fix (feel free to link to code where relevant). Screenshots/GIFs are also fine here.