Log (history) for entity changes

[michaelbromley]

Is your feature request related to a problem? Please describe.
An Order changes state during processing. We need a log of these changes so for auditing purposes, including date, administrator, and other contextual information. E.g.

• Order transitioned to PaymentAuthorized state on xxxxx date
• Order transitioned to PaymentSettled state one xxxx date by administrator Joe.

This would allow us to implement an Order History like Shopify do:

Same also goes for Payment entities. Generalizing this, it might also be useful to log changes to other entities such as Customer or ProductVariant. We'd need to strike a balance here because for certain frequently-changing entities this could generate a log of only marginally-useful noise.

Describe the solution you'd like
A new entity, LogEntry which contains things like date, user, event type, contextual info. An interface Loggable could be implemented by entities which should be logged:

interface Loggable {
  log: LogEntry[]
}

Need to figure out whether a single entity would work with the various types of log message that might be needed, or whether inheritance would be better.

[michaelbromley]

What to log?

Some of the things that should be logged to the history for an Order:

• State transitions
• Payment authorized
• Payment settled
• Fulfillment created
• Cancellation
• Refund created
• Refund settled
• Notes by admin

Common fields

• id
• createdAt
• updatedAt
• Administrator (who instigated the action, get from the RequestContext)

Since each type of log entry would have other different fields, it might make sense to just dump related data (refundId for refunds, fulfillmentId for fulfillments etc) into a stringified JSON field and use a discriminator + unions for the purposes of type safety. Also the GraphQL type could also just use the JSON type to expose whatever data is needed.