AWS workflow

[borisliao]

This is part 2 of 2 for adding the AWS workflow to GitHub Actions.

File Description:

• task_definition.json - AWS ECS format to orchestrate a new Dockerfile
• aws.yml - GitHub Actions workflow file
• Dockerfile - Docker setup file for bot
• webhook_messenger.py - File GitHub Actions calls though aws.yml to request the currently running bot to shut down gracefully.

Merge #84 before merging this PR so that GitHub Actions can request the currently running bot to shut down gracefully.