Support checking out msft repo. (sonic-net#16668)

What is the motivation for this PR?
To enable PR testing in the msft repo, we need to ensure support for checking out its code. This PR introduces the way to enable code checkout for the msft repo.

How did you do it?
If repo_name contains msft, we will check out msft test repo.

How did you verify/test it?
Test by pipeline.

.azure-pipelines/test_plan.py

@@ -27,7 +27,9 @@
 BUILDIMAGE_REPO_FLAG = "buildimage"
 MGMT_REPO_FLAG = "sonic-mgmt"
 INTERNAL_REPO_LIST = ["Networking-acs-buildimage", "sonic-mgmt-int"]
+MSFT_REPO_FLAG = "msft"
 GITHUB_SONIC_MGMT_REPO = "https://github.com/sonic-net/sonic-mgmt"
+GITHUB_SONIC_MGMT_REPO_MSFT = "https://github.com/Azure/sonic-mgmt.msft"
 INTERNAL_SONIC_MGMT_REPO = "https://dev.azure.com/mssonic/internal/_git/sonic-mgmt-int"
 PR_TEST_SCRIPTS_FILE = "pr_test_scripts.yaml"
 SPECIFIC_PARAM_KEYWORD = "specific_param"
@@ -276,7 +278,11 @@ def create(self, topology, test_plan_name="my_test_plan", deploy_mg_extra_params
 
         # If triggered by the internal repos, use internal sonic-mgmt repo as the code base
         sonic_mgmt_repo_url = GITHUB_SONIC_MGMT_REPO
-        if kwargs.get("source_repo") in INTERNAL_REPO_LIST:
+
+        if MSFT_REPO_FLAG in repo_name:
+            sonic_mgmt_repo_url = GITHUB_SONIC_MGMT_REPO_MSFT
+
+        elif kwargs.get("source_repo") in INTERNAL_REPO_LIST:
             sonic_mgmt_repo_url = INTERNAL_SONIC_MGMT_REPO
 
         # If triggered by mgmt repo, use pull request id as the code base