Add missing counter field support to some aggregations.

[martijnvg]

This adds missing counter field support to min, max and top_metrics aggregations.

Not all aggregations support field with time_series_metric set to counter.
This is because computing certain aggregations on these counter fields don't make much sense.
For example, computing a sum or avg on a counter field doesn't make sense, because
counter fields are monodically increasing number fields (with sometimes a reset).

However supporting counter field support to min, max and top_metrics aggregations makes sense
and can be useful.

[elasticsearchmachine]

Pinging @elastic/es-analytics-geo (Team:Analytics)

[ruflin]

Did you check by chance if there other aggregations where the counter entry is missing? What about Gauge?

The previous error message was a bit tricky to understand. Could we also improve this?

[martijnvg]

Did you check by chance if there other aggregations where the counter entry is missing?

I think with this change counter fields are supported by the following aggregations: rate, histogram, range,
min, max, top_metrics and variable_width_histogram.

The previous error message was a bit tricky to understand. Could we also improve this?

I will address this in a follow up.

[romseygeek]

LGTM!