Refactor prepare-pipelines.yml (#1668)

eng/pipelines/prepare-pipelines.yml

@@ -1,10 +1,9 @@
 trigger: none
 
+variables:
+- template: /eng/pipelines/templates/variables/image.yml
+
 extends:
   template: /eng/common/pipelines/templates/jobs/prepare-pipelines.yml
   parameters:
-    Repository: $(Build.Repository.Name)
-    Prefix: android
-    CIConventionOptions: ''
-    UPConventionOptions: '--variablegroups 1 58 76'
-    TestsConventionOptions: ''
+    Repository: Azure/azure-sdk-for-android

eng/pipelines/templates/variables/image.yml

@@ -0,0 +1,28 @@
+# Default pool image selection. Set as variable so we can override at pipeline level
+
+variables:
+  - name: LINUXPOOL
+    value: azsdk-pool-mms-ubuntu-2004-general
+  - name: LINUXNEXTPOOL
+    value: azsdk-pool-mms-ubuntu-2204-general
+  - name: WINDOWSPOOL
+    value: azsdk-pool-mms-win-2022-general
+  - name: MACPOOL
+    value: Azure Pipelines
+
+  - name: LINUXVMIMAGE
+    value: azsdk-pool-mms-ubuntu-2004-1espt
+  - name: LINUXNEXTVMIMAGE
+    value: azsdk-pool-mms-ubuntu-2204-1espt
+  - name: WINDOWSVMIMAGE
+    value: azsdk-pool-mms-win-2022-1espt
+  - name: MACVMIMAGE
+    value: macos-latest
+
+  # Values required for pool.os field in 1es pipeline templates
+  - name: LINUXOS
+    value: linux
+  - name: WINDOWSOS
+    value: windows
+  - name: MACOS
+    value: macOS