Create Lambda function which indexes todo's data

[MatthewCYLau]

• Create Lambda function; add function inside of ES VPC
• Add S3 upload event trigger to Lamdba function; listens to upload of .csv files to data folder

Reference documentation:

• Elasticsearch client to index document https://github.com/elastic/elasticsearch-js#quick-start
• Lambda S3 event trigger: https://docs.aws.amazon.com/lambda/latest/dg/with-s3-example.html
• Lambda reads file from S3: https://stackoverflow.com/questions/27299139/read-file-from-aws-s3-bucket-using-node-fs
• Stackoverflow: https://stackoverflow.com/questions/7431268/how-to-read-data-from-csv-file-using-javascript