Refactor existing Self-Monitor (Prometheus) alerts

[TeodorSAP]

The existing self-monitor alerts, based on PromQL queries, should be refactored such that:

• A single PromQL query (i.e. alert) is mapped to each unhealthy condition (i.e. no Go code is involved in logically evaluating the firing alerts)
• The for clause is used to avoid timing issues (where justified)
• Alerts in firing state should strictly be used for negative/unhealthy scenarios

This refactoring should follow the changes introduced in: #1397