Add checkout optional sonic-mgmt param in PR test template (#21224)

What is the motivation for this PR?
In other repos, if we want to use PR test template to run KVM tests, we need to checkout sonic-mgmt first to execute PR test related yaml and python files.

How did you do it?
CHECKOUT_SONIC_MGMT was defined but not used, use CHECKOUT_SONIC_MGMT to allow other repos to checkout sonic-mgmt code.

How did you verify/test it?
PR test passed means it won't affect PR test.
Tested in pipeline to let buildimage to use the template.

Author: xwjiang-ms

.azure-pipelines/pr_test_template.yml

@@ -53,6 +53,10 @@ jobs:
     continueOnError: false
     pool: sonic-ubuntu-1c
     steps:
+      - ${{ if eq(parameters.CHECKOUT_SONIC_MGMT, true) }}:
+        - checkout: ${{ parameters.SONIC_MGMT_NAME }}
+          displayName: "Checkout sonic-mgmt repository"
+
       - template: impacted_area_testing/get-impacted-area.yml
         parameters:
           BUILD_BRANCH: $(BUILD_BRANCH)
@@ -69,6 +73,10 @@ jobs:
     continueOnError: false
     pool: sonic-ubuntu-1c
     steps:
+      - ${{ if eq(parameters.CHECKOUT_SONIC_MGMT, true) }}:
+        - checkout: ${{ parameters.SONIC_MGMT_NAME }}
+          displayName: "Checkout sonic-mgmt repository"
+
       - template: impacted_area_testing/calculate-instance-numbers.yml
         parameters:
           TOPOLOGY: t0
@@ -101,6 +109,10 @@ jobs:
     continueOnError: false
     pool: sonic-ubuntu-1c
     steps:
+      - ${{ if eq(parameters.CHECKOUT_SONIC_MGMT, true) }}:
+        - checkout: ${{ parameters.SONIC_MGMT_NAME }}
+          displayName: "Checkout sonic-mgmt repository"
+
       - template: impacted_area_testing/calculate-instance-numbers.yml
         parameters:
           TOPOLOGY: t0-2vlans
@@ -134,6 +146,10 @@ jobs:
     continueOnError: false
     pool: sonic-ubuntu-1c
     steps:
+      - ${{ if eq(parameters.CHECKOUT_SONIC_MGMT, true) }}:
+        - checkout: ${{ parameters.SONIC_MGMT_NAME }}
+          displayName: "Checkout sonic-mgmt repository"
+
       - template: impacted_area_testing/calculate-instance-numbers.yml
         parameters:
           TOPOLOGY: t1
@@ -166,6 +182,10 @@ jobs:
     continueOnError: false
     pool: sonic-ubuntu-1c
     steps:
+      - ${{ if eq(parameters.CHECKOUT_SONIC_MGMT, true) }}:
+        - checkout: ${{ parameters.SONIC_MGMT_NAME }}
+          displayName: "Checkout sonic-mgmt repository"
+
       - template: impacted_area_testing/calculate-instance-numbers.yml
         parameters:
           TOPOLOGY: dualtor
@@ -198,6 +218,10 @@ jobs:
     continueOnError: false
     pool: sonic-ubuntu-1c
     steps:
+      - ${{ if eq(parameters.CHECKOUT_SONIC_MGMT, true) }}:
+        - checkout: ${{ parameters.SONIC_MGMT_NAME }}
+          displayName: "Checkout sonic-mgmt repository"
+
       - template: impacted_area_testing/calculate-instance-numbers.yml
         parameters:
           TOPOLOGY: t0-sonic
@@ -235,6 +259,10 @@ jobs:
     continueOnError: false
     pool: sonic-ubuntu-1c
     steps:
+      - ${{ if eq(parameters.CHECKOUT_SONIC_MGMT, true) }}:
+        - checkout: ${{ parameters.SONIC_MGMT_NAME }}
+          displayName: "Checkout sonic-mgmt repository"
+
       - template: impacted_area_testing/calculate-instance-numbers.yml
         parameters:
           TOPOLOGY: dpu
@@ -271,6 +299,10 @@ jobs:
     continueOnError: false
     pool: sonic-ubuntu-1c
     steps:
+      - ${{ if eq(parameters.CHECKOUT_SONIC_MGMT, true) }}:
+        - checkout: ${{ parameters.SONIC_MGMT_NAME }}
+          displayName: "Checkout sonic-mgmt repository"
+
       - template: impacted_area_testing/calculate-instance-numbers.yml
         parameters:
           TOPOLOGY: t1
@@ -304,6 +336,10 @@ jobs:
     continueOnError: false
     pool: sonic-ubuntu-1c
     steps:
+      - ${{ if eq(parameters.CHECKOUT_SONIC_MGMT, true) }}:
+        - checkout: ${{ parameters.SONIC_MGMT_NAME }}
+          displayName: "Checkout sonic-mgmt repository"
+
       - template: impacted_area_testing/calculate-instance-numbers.yml
         parameters:
           TOPOLOGY: t2