[CI/CD] Migrate to SONiC Elastictest (sonic-net#8465)

Approach
What is the motivation for this PR?
Migrate to SONiC Elastictest

co-authorized by: jianquanye@microsoft.com

Author: yejianquan

azure-pipelines.yml

@@ -21,7 +21,6 @@ name: $(TeamProject)_$(Build.DefinitionName)_$(SourceBranchName)_$(Date:yyyyMMdd
 stages:
 - stage: Pre_test
   variables:
-  - group: Testbed-Tools
   - group: GIT_SECRETS
   jobs:
   - job: static_analysis
@@ -44,7 +43,7 @@ stages:
   dependsOn: Pre_test
   condition: and(succeeded(), in(dependencies.Pre_test.result, 'Succeeded'))
   variables:
-  - group: Testbed-Tools
+  - group: SONiC-Elastictest
   - name: inventory
     value: veos_vtb
   - name: testbed_file