Update PlanVersion model to send SNS messages instead of writing to Dynamo

[briri]

Update the PlanVersion's create and update functions to send an SNS message instead of updating the Dynamo table directly.

This will require the creation of a new snsService. See the "Publish" example in the official docs

We will need to add the SNS_TOPIC_ARN env parameter.

We will want to use the new env parameter and"detail_type": "dmp_dynamo_sync", "detail": { "planId": 12345, "jti": "[the current JTI]" } in the message. It will trigger the Lambda that coverts the Plan into the RDA common standard and generates a new plan version in the Dynamo table.