[Metrics UI] Better system for showing autocomplete options in the metrics explorer

[jasonrhodes]

In #57733, we discussed some problems with UX in the Metric Explorer, when we removed group by fields from the "graph per" autocomplete. Fields were being filtered out because we believed they were not relevant fields that could be grouped on. In most cases, this was right, but in a few edge cases where it was wrong, we blocked users from using the Metric Explorer.

The field filtering was removed for performance reasons, but we should investigate and discuss some options for making this experience better for users, because showing ALL fields alphabetically isn't great either.

The best option I can think of is to hard-code or derive some kind of list of "recommended" options which we think are the most likely to be used and include them at the top of the autocomplete list, but still include the rest below, so nobody is blocked.

Thoughts?

[elasticmachine]

Pinging @elastic/logs-metrics-ui (Team:logs-metrics-ui)

[smith]

Not prioritizing this at this time.