CI: Use shared buildkite pipeline vars file

For more info see: https://github.com/wordpress-mobile/
WordPress-Login-Flow-Android/pull/151#issuecomment-2225299197

.buildkite/pipeline.yml

@@ -1,26 +1,21 @@
 # yaml-language-server: $schema=https://raw.githubusercontent.com/buildkite/pipeline-schema/main/schema.json
 ---
 
-common_params:
-  # Common plugin settings to use with the `plugins` key.
-  - &common_plugins
-    - automattic/a8c-ci-toolkit#3.4.2
-
 agents:
   queue: "android"
 
 steps:
   - label: "Gradle Wrapper Validation"
     command: |
       validate_gradle_wrapper
-    plugins: *common_plugins
+    plugins: [$CI_TOOLKIT]
 
   # Wait for Gradle Wrapper to be validated before running any other jobs
   - wait
 
   - label: "Lint & Checkstyle"
     key: "lint_and_checkstyle"
-    plugins: *common_plugins
+    plugins: [$CI_TOOLKIT]
     command: |
       cp gradle.properties-example gradle.properties
       ./gradlew lintRelease checkstyle
@@ -29,7 +24,7 @@ steps:
       - "**/build/reports/checkstyle/checkstyle.*"
   - label: "Test"
     key: "test"
-    plugins: *common_plugins
+    plugins: [$CI_TOOLKIT]
     command: |
       cp gradle.properties-example gradle.properties
       ./gradlew testRelease
@@ -38,7 +33,7 @@ steps:
     depends_on:
       - "lint_and_checkstyle"
       - "test"
-    plugins: *common_plugins
+    plugins: [$CI_TOOLKIT]
     command: |
       cp gradle.properties-example gradle.properties
       ./gradlew \

.buildkite/schedules/dependency-analysis.yml

@@ -1,11 +1,6 @@
 # yaml-language-server: $schema=https://raw.githubusercontent.com/buildkite/pipeline-schema/main/schema.json
 ---
 
-common_params:
-  # Common plugin settings to use with the `plugins` key.
-  - &common_plugins
-    - automattic/a8c-ci-toolkit#3.4.2
-
 agents:
   queue: "android"
 
@@ -15,7 +10,7 @@ steps:
       echo "--- 📊 Analyzing"
       cp gradle.properties-example gradle.properties
       ./gradlew buildHealth
-    plugins: *common_plugins
+    plugins: [$CI_TOOLKIT]
     artifact_paths:
       - "build/reports/dependency-analysis/build-health-report.*"
     notify:

.buildkite/shared-pipeline-vars

@@ -0,0 +1,6 @@
+#!/bin/sh
+
+ # This file is `source`'d before calling `buildkite-agent pipeline upload`, and can be used
+ # to set up some variables that will be interpolated in the `.yml` pipeline before uploading it.
+
+ export CI_TOOLKIT="automattic/a8c-ci-toolkit#3.4.2"