[kube-prometheus-stack] Add interval field for default dashboards

[ecd0011]

What this PR does / why we need it

This PR adds support for configuring the interval value used in Grafana dashboards through a new Helm value grafana.defaultDashboardsInterval.

Many Grafana dashboards in the chart have hardcoded "interval": "1m" values, which limits the resolution of metrics displayed regardless of your Prometheus scrape interval. If you're using a lower scrape interval (like 10s or 30s), you're missing out on higher resolution data that's already being collected.

This allows you to configure by making the interval configurable via Helm values, similar to how dashboard editability is already handled using the sync_grafana_dashboards.py script.

Checklist

• DCO signed
• Chart Version bumped
• Title of the PR starts with chart name (e.g. [prometheus-couchdb-exporter])

[QuentinBisson]

Looks quite good to me

[QuentinBisson]

Can you please fix the linting?

[jkroepke]

hyper theoretically, Using $__rate_interval would be a better option? A better default value?

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

[QuentinBisson]

@ecd0011 would you be able to do the same for the $__rate_interval?

[ecd0011]

@jkroepke It seems like they're serving different purposes.

interval in terms of this PR is adjusting how often the queries themselves are ran. $__rate_interval is only supported for Prometheus data sources and is meant to be used in the rate function for queries: https://grafana.com/docs/grafana/latest/dashboards/variables/add-template-variables/#__rate_interval

In other words, interval is determining when the query is executed, but not what the query retrieves. $__rate_interval helps determine what the query retrieves, but not how often it's executed.

@QuentinBisson given the documentation @jkroepke sent recommends to use the $__rate_interval for certain query functions, I'd suggest leaving it using that variable and letting Prometheus determine what the value of that should be.

[jkroepke]

thanks for clarifications! Absolute right. I thought the PR is doing something like

rate(prometheus_values[{{ $.Values.grafana.defaultDashboardsInterval}}])