SQL: change date_histogram to stop using deprecated "interval"

[astefan]

Following #33727 the interval has been considered deprecated in favor of calendar_interval and fixed_interval. For 8.x and 7.2+, we should make the change in SQL as well.

This, also, brings another interesting side effect: lack of tests that check the response headers of sql requests.

warning →299 Elasticsearch-8.0.0-SNAPSHOT-e1e3c61 "[interval] on [date_histogram] is deprecated, use [fixed_interval] or [calendar_interval] in the future."

The deprecation message is being transmitted as an http header and we should check the expected, if not already done, list of incoming headers in our tests.

[elasticmachine]

Pinging @elastic/es-search