[MONIT-4040] Add Push Gateway Component

This merge request introduces a Push Gateway component to enhance metrics collection in the cluster, allowing applications to push metrics to IT Monitoring infrastructure where direct scraping is not feasible. Key changes include deployment, configuration, and documentation updates.

Summary of Changes

• New Deployment: Adds a Kubernetes deployment for a single replica of Prometheus Push Gateway.
• Ingress and Service Setup: Configures a service and optional ingress to enable external access to the Push Gateway. Supports custom hosts, TLS, and path configurations.
• ServiceMonitor Integration: Adds a ServiceMonitor resource to allow Prometheus to scrape metrics from the Push Gateway.
• Documentation: Updates metrics.md with configuration details for enabling and customizing the Push Gateway.
• Helm Values: Adds a configurable pushgateway section in values.yaml for custom image, resource limits, and ingress options.

Testing

• Local deployment and testing using helm install, verified functionality and connectivity.

References

• JIRA: MONIT-4040