Add three stage pipeline template

changelogs/unreleased/three-stage-pipeline-template.yml

+---
+title: Add 3 stage pipeline template
+merge_request: 61762
+author:
+type: added

lib/gitlab/ci/templates/Getting-started.yml

+# This is a sample GitLab CI/CD configuration file that should run without any modifications.
+# It demonstrates a basic 3 stage CI/CD pipeline. Instead of real tests or scripts,
+# it uses echo commands to simulate the pipeline execution.
+#
+# A pipeline is composed of independent jobs that run scripts, grouped into stages.
+# Stages run in sequential order, but jobs within stages run in parallel.
+#
+# For more information, see: https://docs.gitlab.com/ee/ci/yaml/README.html#stages
+
+stages:          # List of stages for jobs, and their order of execution
+  - build
+  - test
+  - deploy
+
+build-job:       # This job runs in the build stage, which runs first.
+  stage: build
+  script:
+    - echo "Compiling the code..."
+    - echo "Compile complete.
+
+unit-test-job:   # This job runs in the test stage.
+  stage: test    # It only starts when the job in the build stage completes successfully.
+  script:
+    - echo "Running unit tests... This will take about 60 seconds."
+    - sleep 60
+    - echo "Code coverage is 90%"
+
+lint-test-job:   # This job also runs in the test stage.
+  stage: test    # It can run at the same time as unit-test-job (in parallel).
+  script:
+    - echo "Linting code... This will take about 10 seconds."
+    - sleep 10
+    - echo "No lint issues found."
+
+deploy-job:      # This job runs in the deploy stage.
+  stage: deploy  # It only runs when *both* jobs in the test stage complete successfully.
+  script:
+    - echo "Deploying application..."
+    - echo "Application successfully deployed."