K6 load test POC

[bcb37]

This adds configuration for running k6 load tests using Upgrade typescript client library methods and two example tests:

• A test using client library methods with some example thresholds
• A test with 2 scenarios, one simulating regular API calls from an application, and another simulating the periodic mathia lambda batch log calls.

To build and run these tests (after installing the deps), in the k6 directory do
npm run build
k6 run dist/<name_of_test>.js

To stream real-time granular results to New Relic, the instruction here using the 'k6_upgrade' API key, which can be found in New Relic under -> 'API Keys'.