Support formatting on datehistogram aggregations

[altanozlu]

Is your feature request related to a problem? Please describe.
I'm trying to make ES endpoints more compatible, I'm intended to use grafana's elasticsearch plugin with quickwit, my goal isn't to replace quickwit plugin, but just to have backward compatibility. Currently grafana's ES plugin uses epoch_millis as a format for datehistograms and tantivy doesn't support format option in datehistograms.

Describe the solution you'd like
I would like to be able to give a optional date formatter function/trait to tantivy aggregations.

Describe alternatives you've considered
Having common datetime formatter/parser crate between tantivy and quickwit.

Additional context
I would like to implement it myself :)