Add config option for disabling reporting

[sed-i]

Issue

By default, grafana sends out anonymous usage stats. This may be undesired in hardened environments.

Solution

Add charm config option to disable reporting.

• In grafana's config file, this option is called reporting_enabled (ref), while in grafana-agent there's a cli flag called -disable-reporting. We want to be consistent across charms, as well as use a positive rather than negative term, for simplicity. So we'll go with reporting_enabled everywhere.
• There is asymmetry between reporting_enabled=true and reporting_enabled=false: when true, we do not render any config, so grafana will use default values; when false, we disable both reporting and plugin update checks. This is desirable because:
  • Having a single config option (at least for now) is a simple solution that covers most use cases.
  • If an admin needs to disable reporting, it is also likely they would like to prevent auto checking for plugin updates.
  • In the future we could add another config option for plugin checks without any breaking changes.

In tandem with:

• Add config option for disabling reporting grafana-agent-k8s-operator#326
• (Also for Loki: https://grafana.com/docs/loki/latest/configure/#analytics)

Fixes #353.

Context

• ADR

Testing Instructions

Upgrade Notes