fix(azure): set diagnostic setting to allow query perf insights (#1422)

<!--- Provide a general summary of your changes in the Title above -->

## Description

<!--- Describe your changes in detail -->

We need to enable diagnostic setting in order to enable query
performance insight. Added manually in portal, but finally found out how
to do it in Bicep:):)

## Related Issue(s)

- #{issue number}

## Verification

- [ ] **Your** code builds clean without any errors or warnings
- [ ] Manual testing done (required)
- [ ] Relevant automated test added (if you find this hard, leave it and
we'll help out)

## Documentation

- [ ] Documentation is updated (either in `docs`-directory, Altinnpedia
or a separate linked PR in
[altinn-studio-docs.](https://github.com/Altinn/altinn-studio-docs), if
applicable)


<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

- **New Features**
- Enhanced monitoring for PostgreSQL resources through integration with
Application Insights.
- Added diagnostic settings for performance insights, including
configurable log categories and metrics.
  
- **Updates**
- Connection strings for PostgreSQL and Redis are now securely stored as
references in Key Vault.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

.azure/infrastructure/main.bicep

@@ -204,6 +204,7 @@ module postgresql '../modules/postgreSql/create.bicep' = {
       ? srcKeyVaultResource.getSecret('dialogportenPgAdminPassword${environment}')
       : secrets.dialogportenPgAdminPassword
     sku: postgresConfiguration.sku
+    appInsightWorkspaceName: appInsights.outputs.appInsightsWorkspaceName
     enableQueryPerformanceInsight: postgresConfiguration.enableQueryPerformanceInsight
     subnetId: vnet.outputs.postgresqlSubnetId
     vnetId: vnet.outputs.virtualNetworkId

.azure/modules/postgreSql/create.bicep

@@ -34,6 +34,9 @@ param sku Sku
 @description('Enable query performance insight')
 param enableQueryPerformanceInsight bool
 
+@description('The name of the Application Insights workspace')
+param appInsightWorkspaceName string
+
 @description('The Key Vault to store the PostgreSQL administrator login password')
 @secure()
 param srcKeyVault object
@@ -136,6 +139,46 @@ resource pgms_wait_sampling_query_capture_mode 'Microsoft.DBforPostgreSQL/flexib
   }
 }
 
+resource appInsightsWorkspace 'Microsoft.OperationalInsights/workspaces@2023-09-01' existing = {
+  name: appInsightWorkspaceName
+}
+
+// todo: setting as 0 for now. Will use the log analytics workspace policy instead. Consider setting explicitly in the future.
+var diagnosticSettingRetentionPolicy = {
+  days: 0
+  enabled: false
+}
+
+var diagnosticLogCategories = [
+  'PostgreSQLLogs'
+  'PostgreSQLFlexSessions'
+  'PostgreSQLFlexQueryStoreRuntime'
+  'PostgreSQLFlexQueryStoreWaitStats'
+  'PostgreSQLFlexTableStats'
+  'PostgreSQLFlexDatabaseXacts'
+]
+
+resource diagnosticSetting 'Microsoft.Insights/diagnosticSettings@2021-05-01-preview' = if (enableQueryPerformanceInsight) {
+  name: 'PostgreSQLDiagnosticSetting'
+  scope: postgres
+  properties: {
+    workspaceId: appInsightsWorkspace.id
+    logs: [for category in diagnosticLogCategories: {
+      category: category
+      enabled: true
+      retentionPolicy: diagnosticSettingRetentionPolicy
+    }]
+    metrics: [
+      {
+        timeGrain: null
+        enabled: true
+        retentionPolicy: diagnosticSettingRetentionPolicy
+        category: 'AllMetrics'
+      }
+    ]
+  }
+}
+
 module adoConnectionString '../keyvault/upsertSecret.bicep' = {
   name: 'adoConnectionString'
   params: {