azurerm_application_gateway - support for the Basic SKU (#27440)

* feat: #25973 azurerm_application_gateway basic sku support

* feat: #25973 additional checks for application gateway Basic SKU supported features

* tests: #25973 add tests for application gateway basic sku

* fix: #2597 revert erroneous markdown lint changes

* docs: #2597 add Basic SKU docs

* tests(application_gateway): #25973 update tests to use v2 SKUs as V1 is now deprecated

See https://learn.microsoft.com/en-us/azure/application-gateway/v1-retirement#retirement-timelines

* tests(application_gateway): #25973 update all agw tests to include priority on request_routing_rule as required with agw v2 sku

* tests(application_gateway): #25973 update test public ip resource to be standard sku for compatibility with agw v2

internal/services/network/application_gateway_resource.go

@@ -811,6 +811,7 @@ func resourceApplicationGateway() *pluginsdk.Resource {
 							Type:     pluginsdk.TypeString,
 							Required: true,
 							ValidateFunc: validation.StringInSlice([]string{
+								string(applicationgateways.ApplicationGatewaySkuNameBasic),
 								string(applicationgateways.ApplicationGatewaySkuNameStandardSmall),
 								string(applicationgateways.ApplicationGatewaySkuNameStandardMedium),
 								string(applicationgateways.ApplicationGatewaySkuNameStandardLarge),
@@ -825,6 +826,7 @@ func resourceApplicationGateway() *pluginsdk.Resource {
 							Type:     pluginsdk.TypeString,
 							Required: true,
 							ValidateFunc: validation.StringInSlice([]string{
+								string(applicationgateways.ApplicationGatewayTierBasic),
 								string(applicationgateways.ApplicationGatewayTierStandard),
 								string(applicationgateways.ApplicationGatewayTierStandardVTwo),
 								string(applicationgateways.ApplicationGatewayTierWAF),
@@ -4709,12 +4711,45 @@ func checkSslPolicy(sslPolicy []interface{}) error {
 	return nil
 }
 
+func checkBasicSkuFeatures(d *pluginsdk.ResourceDiff) error {
+	_, hasAutoscaleConfig := d.GetOk("autoscale_configuration.0")
+	if hasAutoscaleConfig {
+		return fmt.Errorf("The Application Gateway does not support `autoscale_configuration` blocks for the selected SKU tier %q", applicationgateways.ApplicationGatewaySkuNameBasic)
+	}
+
+	capacity, hasCapacityConfig := d.GetOk("sku.0.capacity")
+	if hasCapacityConfig {
+		if capacity.(int) > 2 || capacity.(int) < 1 {
+			return fmt.Errorf("`capacity` value %q for the selected SKU tier %q is invalid. Value must be between [1-2]", capacity, applicationgateways.ApplicationGatewaySkuNameBasic)
+		}
+	} else {
+		return fmt.Errorf("The Application Gateway must specify a `capacity` value between [1-2] for the selected SKU tier %q", applicationgateways.ApplicationGatewaySkuNameBasic)
+	}
+
+	_, hasMtlsConfig := d.GetOk("trusted_client_certificate")
+	if hasMtlsConfig {
+		return fmt.Errorf("The Application Gateway does not support `trusted_client_certificate` blocks for the selected SKU tier %q", applicationgateways.ApplicationGatewaySkuNameBasic)
+	}
+
+	_, hasRewriteRuleSetConfig := d.GetOk("rewrite_rule_set")
+	if hasRewriteRuleSetConfig {
+		return fmt.Errorf("The Application Gateway does not support `rewrite_rule_set` blocks for the selected SKU tier %q", applicationgateways.ApplicationGatewaySkuNameBasic)
+	}
+
+	return nil
+}
+
 func applicationGatewayCustomizeDiff(ctx context.Context, d *pluginsdk.ResourceDiff, _ interface{}) error {
 	_, hasAutoscaleConfig := d.GetOk("autoscale_configuration.0")
 	capacity, hasCapacity := d.GetOk("sku.0.capacity")
 	tier := d.Get("sku.0.tier").(string)
 
-	if !hasAutoscaleConfig && !hasCapacity {
+	if tier == string(applicationgateways.ApplicationGatewaySkuNameBasic) {
+		err := checkBasicSkuFeatures(d)
+		if err != nil {
+			return err
+		}
+	} else if !hasAutoscaleConfig && !hasCapacity {
 		return fmt.Errorf("The Application Gateway must specify either `capacity` or `autoscale_configuration` for the selected SKU tier %q", tier)
 	}