Configure DynamoDB table via Serverless

[elliotdavies]

Slack Monitor uses a DynamoDB table to store authenticated teams. Currently, this is expected to already exist and to be called slackmonitor. The auto-generated IAM role assigned to the Lambda function must also have the correct permissions to read and write to DynamoDB.

It would be much simpler if the DynamoDB table and permissions could automatically be set up through a CloudFormation config in serverless.yml.