Add support to use old ddb stream image for REMOVE events

[graytaylor0]

Description

Adds an option in the to view_on_remove: OLD_IMAGE (defaults to NEW_IMAGE), which will construct an Event from the view type for REMOVE stream events, if old image exists. If it does not exist, the new image will still be used for the Event.

This follows from DynamoDB streams documentation

StreamViewType — Specifies the information that will be written to the stream whenever data in the table is modified:

    KEYS_ONLY — Only the key attributes of the modified item.

    NEW_IMAGE — The entire item, as it appears after it was modified.

    OLD_IMAGE — The entire item, as it appeared before it was modified.

    NEW_AND_OLD_IMAGES — Both the new and the old images of the item

Issues Resolved

Resolves #4261

Check List

• New functionality includes testing.
• New functionality has a documentation issue. Please link to it in this PR.
  • New functionality has javadoc added
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[dlvenable]

DynamoDB supports getting stream records as NEW_IMAGE, OLD_IMAGE, KEYS_ONLY, and NEW_AND_OLD_IMAGES. Do you think there may be value for users in using some of these other configurations? For example, if a user wants to perform some processor comparison between the new and old to create a new value.

If so, should we move this from a boolean to an image_view option?

image_view: old_image

https://docs.aws.amazon.com/amazondynamodb/latest/APIReference/API_streams_StreamRecord.html

We don't have to implement them all now. But, the configuration would be extensible.

[graytaylor0]

There may be room for a more extendible config here, but currently it is required that users have either NEW_AND_OLD_IMAGE or NEW_IMAGE enabled on their streams.

OLD_IMAGE specifically is needed for REMOVE actions, because otherwise an empty item is provided from the stream record.

[graytaylor0]

Maybe something like this mapping makes sense

stream:
   insert_image: new
   modify_image: new
   remove_image: old

[graytaylor0]

We can start with just

stream:
  image_on_remove: old // can be old or new, default to new

This makes the configuration more extendible in the future for something like

stream:
  image_on_insert: new
  image_on_modify: old_and_new
  image_on_remove: old