beta_release-1: PP-9001: add webhook message model for serialised webhook message bod…
…y (#44)
* add webhook message model for serialised webhook message body
Addresses TODO to serialise response in expected format
add missing field 'resource_type' serialised from SQS message and added as top level field to message
Serialises/Deserialises timestamp from SQS message as Instant
* use naming strategy to set field names
* get date and event type from WebhookMessageEntity
* add fields to WebhookEntity and use to serialise webhook message body
* restore comment (as resource still needs more transformation)
rename record to make more specific to Webhook message body.
* assorted changes based on PR comments