docs: interactive aggregation threshold example

[dwootton]

Added the interactive aggregation threshold example from this demo.

[dwootton]

Addressing failed tests rn

[dwootton]

Hmm no errors in editor, is there any known problems with the Node tests failing?

[domoritz]

Received: "must NOT have additional properties, must NOT have additional properties, must NOT have additional properties, must NOT have additional properties, must NOT have additional properties, must NOT have additional properties, must NOT have additional properties, must NOT have additional properties, must be array, must have required property 'data', must have required property 'data', must be object, must be string, must be number, must be boolean, must match exactly one schema in oneOf, must be object, must match exactly one schema in oneOf, must match exactly one schema in oneOf, must have required property 'signal', must match exactly one schema in oneOf, must be equal to one of the allowed values, must be equal to one of the allowed values, must be equal to one of the allowed values, must match exactly one schema in oneOf"

which is super hard to parse. Try making the spec in ts and validate against the Vega-Lite spec type:

vega-lite/src/spec/index.ts

Line 62 in 9930d29

export type TopLevelSpec =