datadog-cr-validate: catch dashboard queries that break when a template variable is set to * #158

What

The dashboard lint in actions/datadog-cr-validate/validate.py (dashboards()) checks only that spec.widgets is a JSON array, that every widget has a definition.type, and that every $variable is declared. It does not fill in template variables or parse the queries that result. The tag check (metric_filters) skips any filter that contains * or $.

Why it matters

DND-IT/launchpad's App Overview dashboard filtered on gateway.k8s.aws.alb/resource:*$namespace.value*. With the variable set to * (the default, or the built-in All entry), the filter became ***. Datadog rejects that query (Rule 'or_op' didn't match at '**}'), so every ALB widget showed no data, and the lint passed it.

Suggested fix

• Lint: flag a template variable wrapped in wildcards (*$var.value*, *$var*), because selecting * always yields ***.
• And/or: fill in each variable's defaults plus *, then run each metric query through POST /api/v1/query (or the scalar/timeseries query API) and fail on parse errors.