Add Forge integration for consuming Grafana alerts and forwarding to PagerDuty

[edersonbrilhante]

Description:
We want Forge to support consuming alerts from Grafana (including Loki and Prometheus sources) and forwarding them to PagerDuty. This would allow our teams to centralize alert notifications and respond faster to critical events, similar to the existing Splunk Cloud/SignalFx integration.

Proposed Work:

• Create a Terraform/Forge module to set up the PagerDuty integration for Grafana alerts.
• Create another module or a set of predefined Grafana alert rules/dashboards that the integration will consume.
• Ensure the integration can handle both metrics-based alerts (Prometheus) and log-based alerts (Loki).
• Include multi-tenant support if needed (similar to how Forge handles other services).

Benefits:

• Centralized alert management for Grafana-based observability.
• Faster incident response.
• Standardized alerts and queries across environments.

Optional:

• Provide a way to configure severity mapping from Grafana alerts to PagerDuty incidents.
• Include documentation and examples for common alert use cases.

Acceptance Criteria:

• Alerts from Grafana (Prometheus/Loki) trigger PagerDuty incidents.
• Modules are reusable and configurable for multiple environments.
• Documentation is provided for setup and usage.