Add Custom Fields to Multiple Entities

[seanbailis]

Is your feature request related to a problem? Please describe.
Unable to directly track incoming / ordered stock directly on a stock level. Unable to store some specific details we want to track on other entities.

Describe the solution you'd like
Please allow for custom fields on the following entities:
• Payment
• Refund
• Session
• ShippingLine
• StockLevel
• StockMovement

Describe alternatives you've considered
Making a custom entities - not ideal.

Additional context
Currently unavailable, console output: "Could not find embedded CustomFields property on entity 'StockLevel'". Same with the other entities.

[mschipperheyn]

We would like to see CustomFields on the HistoryEntry entity. While it already allows you to add a JSON data structure, we wanted to use this entity for a Note/TODO like approach. It would nicely integrate with the CustomerHistory or OrderHistory. For such a scenario, you want to do queries that filter by customFields such as done, which makes much more sense at a column level then having to go into JSONs.