Move from AWS Lambda functions to NestJS app and run on containerised platform

[jch254]

Long term solution

If the 15min timeout issue becomes annoying, this will be the solution to #2.

ECS or something like https://fly.io/

• Create a new Dockerised NestJS app (find appropriate starter)
• Add background queue job on cron schedule for sending digest email for all users stored in persistent Key Value store
• Add endpoint to "sign up" taking username, shipsFrom, destinationEmail and store in persistent Key Value store
• Email user after successful setup and outline Discogs Market Montior and the schedule of emails (including one currently sending)
• Enqueue initial digest send