Mocks for tables-streams invocations

[alexbepple]

Is your feature request related to a problem? Please describe.

I am using tables-streams and have found it difficult to mock their invocations.
As a workaround, I have been using if (event.Records[0].eventSourceARN === 'arn:architect-sandbox') {…} inside the Lambda handler. Cringe.

Describe the solution you'd like

I think it should work the same way it works for other mocks, e.g. queues.
Maybe I am missing something, but I also see no particular value in the predefined mocks for insert, modify & delete events.