[APM] Add Throughput tab to Correlations

[ogupte]

Related: #86477

Along with Latency and Errors, we need to include a section for Throughput in the Correlations flyout. We want to be able to identify which fields have correlations with significant changes in throughput (transaction document count over time) between 2 different windows of time: the currently selected time range, and the comparison time range.

[elasticmachine]

Pinging @elastic/apm-ui (Team:apm)

[botelastic]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[sorenlouv]

This is most likely superseded by the correlations improvement made by the ml team.