Adding secret detection ci template

changelogs/unreleased/207990-secret-detection-ci-template.yml

+---
+title: Add secret detection template
+merge_request: 33869
+author:
+type: added

lib/gitlab/ci/templates/Security/Secret-Detection.gitlab-ci.yml

+# Read more about this feature here: https://docs.gitlab.com/ee/user/application_security/secret_detection
+#
+# Configure the scanning tool through the environment variables.
+# List of the variables: https://gitlab.com/gitlab-org/security-products/secret_detection#available-variables
+# How to set: https://docs.gitlab.com/ee/ci/yaml/#variables
+
+variables:
+  SECURE_ANALYZERS_PREFIX: "registry.gitlab.com/gitlab-org/security-products/analyzers"
+  SECRETS_ANALYZER_VERSION: "3"
+
+secret_detection:
+  stage: test
+  image: "$SECURE_ANALYZERS_PREFIX/secrets:$SECRETS_ANALYZER_VERSION"
+  services: []
+  rules:
+    - if: $SECRET_DETECTION_DISABLED
+      when: never
+    - if: $CI_COMMIT_BRANCH && $GITLAB_FEATURES =~ /\bsecret_detection\b/
+      when: on_success
+  artifacts:
+    reports:
+      secret_detection: gl-secret-detection-report.json
+  script:
+    - /analyzer run