Non-Prometheus support (or at least exclusion)

[rgeyer]

When linting a dashboard which does not use prometheus targets, several linting errors will be returned.

These are not actually errors, they're just prometheus based rules being applied to non-prometheus targets and dashboards.

The linter should allow rules to opt-in to what type of panels/targets it can effectively evaluate for best practice, and simply ignore the rest.

This would mean that running the dashboard linter against a dashboard for which it has no best practices (such as query specific rules for a loki panel, as an example), no errors would be emitted.

In time, this would allow for rules specific to other datasources to be added.