This change adds stats about forecasts, to the jobstats api as well as xpack/_usage. The following
information is collected:
_xpack/ml/anomaly_detectors/{jobid|_all}/_stats:
- total number of forecasts
- memory statistics (mean/min/max)
- runtime statistics
- record statistics
- counts by status
_xpack/usage
- collected by job status as well as overall (_all):
- total number of forecasts
- number of jobs that have at least 1 forecast
- memory, runtime, record statistics
- counts by status
Fixes#31395