Refactor tarball CI build to support both official and public builds (#12668)

eng/source-build-tarball-build-official.yml

@@ -0,0 +1,14 @@
+trigger: none
+pr: none
+resources:
+  pipelines:
+  - pipeline: installer-build-resource
+    source: dotnet-installer-official-ci
+    trigger: true
+
+stages:
+- stage: build
+  jobs:
+  - template: /src/SourceBuild/Arcade/eng/common/templates/job/source-build-run-tarball-build.yml
+    parameters:
+      tarballResourceId: installer-build-resource

eng/source-build-tarball-build.yml

@@ -2,10 +2,7 @@ trigger: none
 pr: none
 resources:
   pipelines:
-  - pipeline: dotnet-installer-official-ci-resource
-    source: dotnet-installer-official-ci
-    trigger: true
-  - pipeline: installer-resource
+  - pipeline: installer-build-resource
     source: installer
     trigger: true
 
@@ -14,7 +11,4 @@ stages:
   jobs:
   - template: /src/SourceBuild/Arcade/eng/common/templates/job/source-build-run-tarball-build.yml
     parameters:
-      ${{ if eq(variables['System.TeamProject'], 'public') }}:
-        tarballResourceId: installer-resource
-      ${{ if eq(variables['System.TeamProject'], 'internal') }}:
-        tarballResourceId: dotnet-installer-official-ci-resource
+      tarballResourceId: installer-build-resource