CE-3034: Fix exporter data dropping
Separated the time-consuming metric calculation from the DB related (quick to calculate) ones.
The time consuming ones are updated by a scheduler, by default ever 2 minutes - the interval can be set in the playbook.
Managed to reduce the response time on TEST environment from ~10 sec to around 240ms (slowest response time was 1.1s, when the metrics page loaded the first time)