[ML] Make file/index data visualizer time field cards more similar

[droberts195]

The index data visualizer's timestamp card for index patterns looks like this:

But the timestamp card for uploaded files in the file data visualizer looks like this:

We discussed this a couple of months ago and decided that the index data visualizer's display, i.e. showing earliest and latest timestamps, is better.

One thing to be aware of is that the file structure finder doesn't read the whole file. So the earliest and latest wouldn't refer to the whole file. However, now that people can change the number of lines to sample in the overrides dialog so that the whole file gets sampled this is probably OK. I guess we could say something like "earliest X, latest Y (based on first N messages in file)" on the card.

The backend change that is required to support this enhancement is elastic/elasticsearch#42890.

[elasticmachine]

Pinging @elastic/ml-ui

[droberts195]

Note: this is not nearly as important as #36880. No time should be spent on this until #36880 is complete.

[peteharverson]

Closing issue as with the redesign of the file data visualizer for 7.12 in #87598, the display for time fields now matches that used in the index version.