Document the default max number of buckets in the auto_date_histogram documentation

[colings86]

Document that max_bucket setting means that by default the max number of buckets you can request in the auto_date_histogram aggregation is 333.

This is because we need collect num_buckets * 30 buckets before we can merge up to the next interval

We should also mention that this limit can be changed using the max_buckets setting

[elasticmachine]

Pinging @elastic/es-search-aggs

[debadair]

[doc issue triage]

See discussion in #28993.

[not-napoleon]

I think we can close this now that we've resolved #57042, which causes max buckets to only be checked during the reduce phase. Feel free to reopen if there's a need, but it seems redundant to me at this point.