[Lens] Support delay agg

[Dosant]

Describe the feature:

Elasticsearch exposes dev only delay agg that is usefull to simulate long-running searches.
Kibana supports this agg in aggregation based visualization, but it would be very helpful to have it in Lens

kibana/src/plugins/data/public/search/search_service.ts

Lines 158 to 161 in 96ddfe6

	if (this.initializerContext.config.get().search.aggs.shardDelay.enabled) {
	aggs.types.registerBucket(SHARD_DELAY_AGG_NAME, getShardDelayBucketAgg);
	expressions.registerFunction(aggShardDelay);
	}

Describe a specific use case for the feature:

Simulate long-running searches in Lens

[elasticmachine]

Pinging @elastic/kibana-app (Team:KibanaApp)

[stratoula]

cc @ghudgins

[flash1293]

This is supported by setting ELASTIC_LENS_DELAY_SECONDS on the window object:

kibana/x-pack/plugins/lens/readme.md

Line 28 in 542b381

To simulate long running searches, set `data.search.aggs.shardDelay.enabled` in your `kibana.dev.yml` to true and set the dealy via console in the browser (e.g. for a 20 seconds delay): `window.ELASTIC_LENS_DELAY_SECONDS=20`.