ci: use ci_toolkit instead of docker

.buildkite/pipeline.yml

@@ -1,13 +1,6 @@
 x-common-params:
-  - &docker-container
-    docker#v3.8.0:
-      image: "public.ecr.aws/automattic/android-build-image:v1.3.0"
-      propagate-environment: true
-      environment:
-       # DO NOT MANUALLY SET THESE VALUES!
-        # They are passed from the Buildkite agent to the Docker container
-        - "AWS_ACCESS_KEY"
-        - "AWS_SECRET_KEY"
+  - &ci_toolkit
+    automattic/a8c-ci-toolkit#3.0.1
   - &nvm_plugin
     automattic/nvm#0.3.0:
       # This is an attempt to fix curl error (92) during installing nodejs.
@@ -19,11 +12,11 @@ steps:
       npm install
       ./gradlew publishToMavenLocal
     plugins:
-      - *docker-container
+      - *ci_toolkit
       - *nvm_plugin
   - label: "Publish to S3"
     plugins:
-      - *docker-container
+      - *ci_toolkit
       - *nvm_plugin
     if: build.branch == "trunk"
     command: |