Propagate defaults from source functions to WidgetSource

[donmccurdy]

Currently we assign defaults in the source functions...

carto-api-client/src/sources/h3-query-source.ts

Lines 35 to 42 in 4d5b9c7

	const {
	aggregationExp,
	aggregationResLevel = DEFAULT_AGGREGATION_RES_LEVEL_H3,
	sqlQuery,
	spatialDataColumn = 'h3',
	queryParameters,
	filters,
	} = options;

... but these defaults are not assigned to the original options object, and so are not passed down into the WidgetSource. To avoid a lot of redundancy assigning the defaults again later for widget-related functions, it would be better if the defaults were assigned once and propagated down into the WidgetSource from there, where more of the properties could be considered 'required'.