AWS DynamoDB + Firebase Integration

Keep AWS DynamoDB and Firebase aligned: use one app's database actions to perform the other's.

Example: use AWS DynamoDB's "Batch Get Items" action to perform Firebase's "Batch Create Users" action. AWS DynamoDB has 21 actions (including Batch Get Items, Batch Write Items, and Create Backup); Firebase has 19 actions (including Batch Create Users, Create Session Cookie, and Create User).