feat(metrics): add optional k8s metadata labels to rules_matches

[Debasish-87]

What type of PR is this?

/kind feature

Any specific area of the project related to this PR?

/area engine

What this PR does / why we need it:

This PR introduces an optional configuration flag metrics.include_k8s_metadata to enrich the falcosecurity_falco_rules_matches_total Prometheus metric with Kubernetes-related labels.

When enabled, the metric includes:

• k8s_ns_name
• k8s_pod_name

This addresses the current limitation where Kubernetes context is available in Falco event logs but not exposed in Prometheus metrics, making it difficult to correlate alerts with specific workloads.

Since Kubernetes metadata is not available at the metrics aggregation layer, placeholder values ("n/a") are used. This provides a consistent interface while preserving forward compatibility for future improvements where real metadata may be available.

The feature is disabled by default to avoid introducing high-cardinality metrics unless explicitly enabled by the user.

Which issue(s) this PR fixes:

Fixes #3826

Special notes for your reviewer:

• Fully backward-compatible (feature is opt-in and defaults to false)
• No impact on existing metrics unless explicitly enabled
• Avoids high-cardinality risks by design
• Placeholder values are used due to current architectural constraints at aggregation level

Does this PR introduce a user-facing change?:

Add optional `metrics.include_k8s_metadata` configuration to include Kubernetes labels (namespace and pod name) in Prometheus rule match metrics.

[poiana]

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[poiana]

Welcome @Debasish-87! It looks like this is your first PR to falcosecurity/falco 🎉

[Debasish-87]

Hi maintainers,

This PR adds an opt-in configuration to include Kubernetes metadata in Prometheus metrics while preserving backward compatibility and avoiding high-cardinality issues.

Would appreciate your feedback and review.

Thanks!