Add pipeline parameter for disabling the VMR build during PRs (#15328)

.vsts-ci.yml

@@ -23,6 +23,11 @@ parameters:
   type: string
   default: $(Build.SourceBranchName)
 
+- name: disableVmrBuild
+  displayName: Skip source-building the VMR
+  type: boolean
+  default: false
+
 variables:
 - name: _PublishUsingPipelines
   value: false
@@ -360,7 +365,16 @@ stages:
 
   - template: /eng/common/templates/jobs/source-build.yml
 
-- ${{ if and(eq(variables['System.TeamProject'], 'internal'), ne(variables['Build.Reason'], 'PullRequest')) }}:
+# You can temporarily disable the VMR Build stage by setting the disableVmrBuild variable on the installer pipeline
+- ${{ if and(eq(variables['Build.Reason'], 'PullRequest'), not(parameters.disableVmrBuild)) }}:
+  - template: eng/pipelines/templates/stages/vmr-build.yml
+    parameters:
+      vmrBranch: ${{ parameters.vmrBranch }}
+      isBuiltFromVmr: false
+
+# In case the VMR Build stage is temporarily disabled, the VMR synchronization step is run to validate
+# that the PR can be merged and later synchronized into the VMR without problems.
+- ${{ else }}:
   - stage: Synchronize_VMR
     displayName: Synchronize VMR
     dependsOn: []
@@ -369,16 +383,6 @@ stages:
       parameters:
         vmrBranch: ${{ parameters.vmrBranch }}
 
-# In case the VMR Build stage needs to be temporarily disabled, please make sure that
-# the VMR synchronization step is run to validate that the PR can be merged and later
-# synchronized into the VMR without problems.
-# You can do this by allowing the Synchronize_VMR stage from above in PRs.
-- ${{ if eq(variables['Build.Reason'], 'PullRequest') }}:
-  - template: eng/pipelines/templates/stages/vmr-build.yml
-    parameters:
-      vmrBranch: ${{ parameters.vmrBranch }}
-      isBuiltFromVmr: false
-
 - ${{ if and(ne(variables['System.TeamProject'], 'public'), notin(variables['Build.Reason'], 'PullRequest')) }}:
   - stage: Publish
     dependsOn: