Change getDateMeta to store interval in custom param

[flash1293]

getDateMeta is a helper to extract the used date histogram of an aggregation out of the data table. It uses the fact that the applied time range is part of the meta data and does the same interval calculation as happening within agg configs.

A cleaner approach is to use a parameter which only gets serialized on the agg config which can easily read without requiring all of the actual logic (like it's done for number histograms: #91370 )

[elasticmachine]

Pinging @elastic/kibana-app-services (Team:AppServices)