Persist state of stream aggregations

[morigs]

Is your feature request related to a problem? Please describe

For aggregations with a big interval it may be important to avoid any losses. Currently, aggregation state is lost on restarts.

Describe the solution you'd like

Perhaps vmagent can periodically save state to the vm and load previous state on start

Describe alternatives you've considered

Right now we're going to use recording rules with backfilling

Additional information

No response