[MONIT-4063] Add Alertmanager to the chart

This merge request introduces support for deploying Alertmanager as part of the Helm chart with flexible configuration options.

Summary of Changes:

• Alertmanager Deployment: Added the option to enable Alertmanager. When enabled, Alertmanager is deployed alongside Prometheus for alert management.
• Ingress Configuration: Configurable to deploy with or without ingress, allowing for flexible external access.
• High Availability (HA) Mode: Configurable for high-availability deployment, ensuring reliable alerting redundancy.

Technical Details:

• New Templates:
  • alertmanager.yaml: Defines the Alertmanager deployment.
  • ingress.yaml: Configures ingress for Alertmanager when enabled.
  • service.yaml: Configures a Kubernetes Service for Alertmanager.
• Prometheus Integration: Updated prometheus.yaml to enable Prometheus to send alerts to Alertmanager if it is deployed.
• Values.yaml: Added configuration options under metrics.alertmanager, enabling customization of image, replicas, node selector, ingress, and HA settings.

Impact:

• Default Behavior: By default, Alertmanager is disabled, ensuring backward compatibility with existing configurations.

Testing:

• Local Helm Installations: Verified functionality through local Helm installations with custom values:
  • Enabled Alertmanager with ingress and confirmed connectivity.
  • Triggered a test Prometheus alert, successfully viewed in Alertmanager.

JIRA References:

• Related to MONIT-4063