victorialogs: gapfill when querying log range stats

Is your feature request related to a problem? Please describe

Output from VictoriaLogs could be improved for Grafana time series panel when values are missing in logs for some time ranges.

Describe the solution you'd like

We are using Grafana datasource which queries log range stats for our time series panels.

It would be great if VictoriaLogs could gapfill the output with null or zero values for ranges with no values.

Describe alternatives you've considered

I didn't find any way to do this using LogsQL.

I tried using Disconnect values feature in Grafana time series panel but it not ideal because it required a static value and breaks when panel interval is bigger than the threshold for disconnecting values.

Additional information

I imagine something like Timescale does with time_bucket_gapfill (docs).

Is this something planned for the future? Would you be open to review a PR if I give this a try?

Start with the VictoriaLogs documentation for querying log range stats and compare the requested behavior with TimescaleDB's time_bucket_gapfill. Locate the log range stats implementation and its tests, then define and verify how empty ranges should be represented as null or zero values.