Utilise serverless-offline-ssm to fix local development

[jch254]

Currently running locally does not work as expected due to incompatibility with serverless-offline and ssm: variables - dherault/serverless-offline#1647. A suggested solution is to use this package https://www.serverless.com/plugins/serverless-offline-ssm

[jch254]

Workaround is to comment SSM vars in serverless.yml. E.g.

functions:
  handler:
    handler: src/index.handler
    memorySize: 256
    timeout: 900
    # environment:
    #   DISCOGS_USER_TOKEN: ${ssm:/discogs-market-monitor/discogs_user_token}
    #   SENDGRID_API_KEY: ${ssm:/discogs-market-monitor/sendgrid_api_key}
    #   DISCOGS_USERNAME: ${ssm:/discogs-market-monitor/discogs_username}
    #   SHIPS_FROM: ${ssm:/discogs-market-monitor/ships_from}
    #   DESTINATION_EMAIL: ${ssm:/discogs-market-monitor/destination_email}
    #   SENDER_EMAIL: ${ssm:/discogs-market-monitor/sender_email}

[jch254]

Using parameter store secrets as done in https://github.com/jch254/market-monitor-api also allows running locally