Add monitor for high GitHub API usage

[zxiiro]

This adds a monitor to alert when unusually high GitHub API usage has been detected.

[Copilot]

Pull Request Overview

This PR adds a Datadog monitor to detect and alert on unusually high GitHub API usage. The monitor is designed to catch potential issues in the ALI system that might cause excessive API calls.

• Adds a new Datadog event-based monitor for GitHub API usage
• Configures alerting thresholds and notification messages
• Provides actionable guidance for investigating high API usage incidents

[github-actions]

OpenTofu plan for prod

Plan: 1 to add, 0 to change, 0 to destroy.

OpenTofu used the selected providers to generate the following execution
plan. Resource actions are indicated with the following symbols:
+   create

OpenTofu will perform the following actions:

  # datadog_monitor.GitHub_API_usage_unusually_high will be created
+   resource "datadog_monitor" "GitHub_API_usage_unusually_high" {
+       evaluation_delay    = (known after apply)
+       id                  = (known after apply)
+       include_tags        = false
+       message             = <<-EOT
            # GitHub API usage is unusually high
            
            We've detected that the GitHub API rate limit usage is higher than usual. This could be an indication of a problem in the ALI system causing higher than expected API calls.
            
            ## Action
            
            Review the rate limit metrics as well as API call count from the ALI for each API call to see if anything unusual is occurring.
        EOT
+       name                = "GitHub API usage unusually high"
+       new_host_delay      = 300
+       notify_no_data      = false
+       query               = "events(\"source:amazon_sns @title:\\\"GitHub API usage unusually high\\\"\").rollup(\"count\").last(\"5m\") > 0"
+       require_full_window = false
+       tags                = (known after apply)
+       type                = "event-v2 alert"

+       monitor_thresholds {
+           critical = "0"
        }
    }

Plan: 1 to add, 0 to change, 0 to destroy.

✅ Plan applied in Tofu Apply #13