docs: add schema v3 example for service definition YAML

- Add comprehensive v3 schema example in resource.tf
- Include v3-specific fields like tier, lifecycle, application, description
- Demonstrate proper v3 syntax and structure for users
- Maintain consistency with existing v2.x examples

Author: samcrudge

examples/resources/datadog_service_definition_yaml/resource.tf

@@ -1,3 +1,55 @@
+// Service Definition with v3 Schema Definition
+resource "datadog_service_definition_yaml" "service_definition_v3" {
+  service_definition = <<EOF
+schema-version: v3
+dd-service: shopping-cart
+team: e-commerce-team
+contacts:
+  - name: Support Email
+    type: email
+    contact: [email protected]
+  - name: Support Slack
+    type: slack
+    contact: https://www.slack.com/archives/shopping-cart
+description: shopping cart service responsible for managing shopping carts
+tier: high
+lifecycle: production
+application: e-commerce
+languages: 
+  - go
+  - python
+type: web 
+ci-pipeline-fingerprints:
+  - fp1 
+  - fp2 
+links:
+  - name: shopping-cart runbook
+    type: runbook
+    url: https://runbook/shopping-cart
+  - name: shopping-cart architecture
+    type: doc
+    provider: gdoc
+    url: https://google.drive/shopping-cart-architecture
+  - name: shopping-cart service Wiki
+    type: doc
+    provider: wiki
+    url: https://wiki/shopping-cart
+  - name: shopping-cart source code
+    type: repo
+    provider: github
+    url: http://github/shopping-cart
+tags:
+  - business-unit:retail
+  - cost-center:engineering
+integrations:
+  pagerduty: 
+    service-url: https://www.pagerduty.com/service-directory/Pshopping-cart
+extensions:
+  mycompany.com/shopping-cart:
+    customField: customValue
+EOF
+}
+
 // Service Definition with v2.2 Schema Definition
 resource "datadog_service_definition_yaml" "service_definition_v2_2" {
   service_definition = <<EOF