dynamodb results split

[twelch]

Resolves #312

Behavior:

• splits results if a metrics array is present, and for more than one sketch.
• groups results by sketchID, and creates a child DB item for each one, that the root DB item tracks using childSketchItems array of sketches.
• Only splits results into multiple dynamodb items if over threshold of 380KB

Testing:

• Adds back tasks class e2e testing using dynamodb-local package.
• adds additional tests for split scenarios