Add rusty-cachier notify job (#11554)

* Add `rusty-cachier notify` job

* Add comments

substrate/.gitlab-ci.yml

@@ -34,6 +34,7 @@ stages:
   - build
   - publish
   - deploy
+  - notify
 
 workflow:
   rules:
@@ -88,6 +89,8 @@ default:
     - rustup +nightly show
     - cargo +nightly --version
 
+# rusty-cachier's hidden job. Parts of this job are used to instrument the pipeline's other real jobs with rusty-cachier
+# Description of the commands is available here - https://gitlab.parity.io/parity/infrastructure/ci_cd/rusty-cachier/client#description
 .rusty-cachier:
   before_script:
     - curl -s https://gitlab-ci-token:${CI_JOB_TOKEN}@gitlab.parity.io/parity/infrastructure/ci_cd/rusty-cachier/client/-/raw/release/util/install.sh | bash
@@ -216,6 +219,16 @@ deploy-prometheus-alerting-rules:
         - .gitlab-ci.yml
         - ./scripts/ci/monitoring/**/*
 
+#### stage:                        notify
+
+# This job notifies rusty-cachier about the latest commit with the cache.
+# This info is later used for the cache distribution and an overlay creation.
+rusty-cachier-notify:
+  stage:                           notify
+  <<:                              *docker-env
+  script:
+    - rusty-cachier cache notify
+
 #### stage:                        .post
 
 # This job cancels the whole pipeline if any of provided jobs fail.