Serverless Implementation: Add event source metadata attributes

[sharvath-newrelic]

Description

Per the Lambda spec, event specific metadata attributes will need to be added depending on the type detected. In addition to instrumentation tests, it would be ideal to have performance/e2e tests set up to vet reception of these attributes on the NR dashboard.

[Newrelic-Boomi]

https://new-relic.atlassian.net/browse/NR-519758