[Metrics UI] Use field caps dataset filtering when possible

[jasonrhodes]

More information on this ticket: #95558 (comment)

We should adopt this so that the long list of autocomplete fields can be improved when we are filtering for certain data in our Metrics UI views. TBD which views and which sets of filters are allowable here.

[Please edit this ticket and the associated AC when we narrow this information down.]

AC:

• Adopt field_caps filtering when loading the autocomplete values, whenever possible

[elasticmachine]

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

[smith]

I'm pretty sure we're already doing this. If not, it's not something we're prioritizing right now.