Add Micro-Benchmarking tests

[KKelvinLo]

What is the Point of this PR This PR adds micro-benchmarking tests for the AWSXRayPropagator, AWSXRayIdgenerator, span creations, and metric creation. The benchmarking library used is benchmark.js.

The list of functions tested and span configurations include:

• start-end sampled span
• start-end un-sampled span
• start-end nested sampled spans
• start-end nested un-sampled spans
• get current span
• add attributes to span
• X-Ray trace id generator - generate trace IDS and span IDS
• X-Ray propagator - inject and extract methods