fix: replace $__interval with $__rate_interval

[kinolaev]

Grafana recommends using $__rate_interval with the rate and increase functions instead of $__interval or a fixed interval value. Since $__rate_interval is always at least four times the scrape interval, it helps avoid issues specific to Prometheus, such as gaps or inaccuracies in query results.

https://grafana.com/docs/grafana/v12.3/datasources/prometheus/template-variables/#use-__rate_interval

[kinolaev]

@itay-grudev , @jsilvela , the PR shouldn't take more than a few minutes of your time) Please have a look

[kinolaev]

@itay-grudev , @jsilvela , I still hope to get a minute of your attention to this tiny PR)