Add documentation to User getExecutionHistory

[hems.io]

I'm creating this issue here so i hopefully be notified when the documentation is updated

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We're looking into just that, as we want to document the columns in a way that is not possible within swagger-ui. We will likely introduce a new folder into this repository and link to it prominently from within the API documentation in the site, the Swagger Explorer, and the README here.

Originally posted by @STRML in #441 (comment)