Add 'gitleaks' job to e3-* repositories

`gitleaks` is a job to detect secret leaks and will especially ensure that
no data on export control policy is pushed to a repository.

> **Note:**
>
> This commit will only add a merge request CI job. Gitleaks needs a
> configuration file to work, and currently, it must first be added to the
> target repository before being able to run the `gitleaks` job.

it/org/software-supply-chain/product-security/issues#71

See merge request it/cookiecutter-e3!89 of the template

Author: cookiecutter-e3

.gitlab-ci.yml

@@ -28,6 +28,11 @@ default:
     - run_as_root:false
   interruptible: true
 
+include:
+  - component: $CI_SERVER_FQDN/it/gitlab-templates/gitleaks@~latest
+    inputs:
+      stage: checks
+
 # Common
 
 .tox-common: