[Github App] AAApiGateway, Github webooks are filtered and fanned out to the correct lambdas.

[lizacullis]

Description:

We already have the basic logic for the fanout pattern in our architecture, but right now we are only processing pull_request events.
We need to add installation and installation_repository to this

Validation steps:
When a user gives the github app access to a repo, that repo is stored in the DynamoDB and displayed on their front-end.

• screenshot of the added repos visible on the front end.

Tech Steps:

• Update the Routing lambda - add installation and installation_repositories to switch statement
• Add functionality to the add repo lambda.
  • Take all the repos from the repositories_added, and add them to the user object in DDB.