APM-5855 make agent pool configurable for testing

Author: sophieclayton12-nhs

azure/common/apigee-build.yml

@@ -30,13 +30,16 @@ parameters:
   - name: python_version
     type: string
     default: "3.8"
+  - name: agent_pool
+    type: string
+    default: "AWS-ECS"
 
 jobs:
   - job: build
     displayName: Build & Test
     timeoutInMinutes: 30
     pool:
-      name: 'AWS-ECS'
+      name: ${{ parameters.agent_pool }}
     workspace:
       clean: all
     variables: