feat(lambda): create lambda for migration of url(s)

[wanlingt]

Problem

Transfer of ownership is currently being done manually and directly in the prod database, which exposes us to unnecessary risks. Further details can be found in the Orphan Links Management Design Doc

Solution

Create an AWS lambda for both types of link transfer operations:

• migrate_url_to_user - to transfer a single link to a new email address (all lowercase)
• migrate_user_links - to transfer all links belonging to an account to another account (all lowercase)

The lambda handler executes the relevant SQL function, using the arguments provided in the event object.

Details:

• The DATABASE_URL env var is provided directly in the lambda's environmental variables configuration, instead of GitHub secrets

Tests

Invoke the test events in each lambda function by filling in the appropriate parameters, and check that the changes are reflected in the database

Deploy Notes

Add serverless deploy to deploy stage for deployment of lambda functions.

Note: deploy-edu remains unchanged.

New environment variables:

• SERVERLESS_STAGE : one of staging, production

New dependencies:

• serverless-plugin-include-dependencies : This Serverless plugin makes deployed functions smaller by only adding the modules relevant to each handler

[LoneRifle]

Lgtm