[multi-asic]: Add job to run multi-asic VS tests in sonic-buildimage pipeline (#11517)

Why I did it
Require multi-asic VS tests to be run during PR checks and merges in master branch.

How I did it
Add job to run multi-asic VS tests in sonic-buildimage pipeline. Currently pipeline will run basic bgp fact test to ensure the testbed comes up, load minigraph works and bgp sessions are up.
Use new multi-asic VS agent pool sonictest-ma in official-multi-asic-vs pipeline
Make multi-asic VS test optional for now. There are two known issues:
Announce route failure during refresh-dut in setup testbed stage.
bgp sessions not getting established.
How to verify it
Tested using test azure pipelines.

.azure-pipelines/official-build-multi-asic.yml

@@ -37,7 +37,7 @@ stages:
 
   jobs:
   - job:
-    pool: sonictest
+    pool: sonictest-ma
     displayName: "kvmtest-multi-asic-t1-lag"
     timeoutInMinutes: 240
 

.azure-pipelines/run-test-template.yml

@@ -51,6 +51,8 @@ steps:
     rm -rf $(Build.ArtifactStagingDirectory)/*
     docker exec sonic-mgmt bash -c "/data/sonic-mgmt/tests/kvmtest.sh -en -T ${{ parameters.tbtype }} ${{ parameters.tbname }} ${{ parameters.dut }} ${{ parameters.section }}"
   displayName: "Run tests"
+  ${{ if eq(parameters.tbtype, 'multi-asic-t1-lag-pr') }}:
+      continueOnError: true
 
 - script: |
     # save dut state if test fails

azure-pipelines.yml

@@ -208,3 +208,17 @@ stages:
         ptf_name: ptf_vms6-1
         tbtype: t0-sonic
         vmtype: vsonic
+
+  - job:
+    pool: sonictest-ma
+    displayName: "kvmtest-multi-asic-t1-lag"
+    timeoutInMinutes: 240
+
+    steps:
+    - template: .azure-pipelines/run-test-template.yml
+      parameters:
+        dut: vlab-08
+        tbname: vms-kvm-four-asic-t1-lag
+        ptf_name: ptf_vms6-4
+        tbtype: multi-asic-t1-lag-pr
+        image: sonic-4asic-vs.img.gz