Add some docs about Logging and Metrics

To leave as examples in case code gets
deleted/forgotten.

Author: Harriethw

docs/infrastructure/metrics-and-logging.md

@@ -0,0 +1,50 @@
+# Metrics and logging
+
+Some processes were setup for the `notifications` code to observe logs, events and metrics
+
+## Application Insights
+
+The ApplicationInsightsLogging service class sets up logs to feed into Application Insights, which can then be called like so:
+
+```
+class CommandHandler:
+    @contextmanager
+    @staticmethod
+    def handle(command_name):
+        try:
+            yield
+            ApplicationInsightsLogging().custom_event_info(
+                event_name=f"{command_name}Completed",
+                message=f"{command_name} completed successfully",
+            )
+        except Exception as e:
+            ApplicationInsightsLogging().exception(f"{command_name}Error: {e}")
+            raise CommandError(e)
+```
+
+
+The Application Insights resource is setup in by the `app_insights_audit` module in terraform:
+
+```
+module "app_insights_audit" {
+  source = "../dtos-devops-templates/infrastructure/modules/app-insights"
+
+  name                = module.shared_config.names.app-insights
+  location            = var.region
+  resource_group_name = azurerm_resource_group.main.name
+  appinsights_type    = "web"
+
+  log_analytics_workspace_id = module.log_analytics_workspace_audit.id
+
+  # alerts
+  action_group_id     = var.action_group_id
+  enable_alerting     = var.enable_alerting
+}
+```
+
+## Metrics
+
+This PR introduced a Metrics service class and command to collect information about queue sizes
+https://github.com/NHSDigital/dtos-manage-breast-screening/pull/617
+
+The metrics would feed through to the Application Insights resource and could be viewed in the Portal.