[WIP] FEATURE: Re-add DynamoDB support.

[tyler-smith]

This change does not remove S3, but adds new lambdas and an API
app that can be used to bypass S3 and maintain a real database of
analytics data in AWS DyanmoDB. It adds and utilizes a generic
store interface that can be used to later add or transition to
different database systems like an RDMS.

Remaining tasks:

• Jest tests for Balance updates/API
• Missing data backfiller
• Test in a real staging environment
  • Create DDB Table
  • Create update lambdas and make sure they work (fix any issues and repeat until done)
  • Create API lambda and make sure it works (fix any issues and repeat until done)
  • Put CloudFront in front of API lambda on a test domain
  • After confirming everything works, redirect api.bitdao.io/analytics to the API lambda.