Snapshot policy support

As described in https://github.com/aws-cloudformation/aws-cloudformation-coverage-roadmap/issues/224, there are resource types that support snapshotting outside of CloudFormation that are missing support for the `Snapshot` policy in [`DeletionPolicy`](https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-attribute-deletionpolicy.html) and [`UpdateReplacePolicy`](https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-attribute-updatereplacepolicy.html), so it'd be great if providers could provide support themselves

Start with the linked CloudFormation coverage-roadmap issue and the referenced DeletionPolicy and UpdateReplacePolicy documentation. Determine how provider support for Snapshot should be represented in the resource schema, and confirm that both policy attributes can express the intended behavior for applicable resource types.

Written by the indexing model from the issue text.