[CICD] Add .gitlab-ci submodule and .gitlab-ci.yml

* The submodule points to the repository containing all CI/CD files
* Insert .gitlab-ci.yml file importing file for automatic manifest
integration

.gitlab-ci @ 943eac76

+Subproject commit 943eac764805a486e3ca2538a263ab531fd4c45b

.gitlab-ci.yml

+---
+# ---------------------------------------------------------------------------------------
+# Include the default CI steps from the gitlab-ci repo
+# ---------------------------------------------------------------------------------------
+include:
+  - project: '${CI_PROJECT_ROOT_NAMESPACE}/infrastructure/gitlab-ci'
+    ref: 943eac764805a486e3ca2538a263ab531fd4c45b
+    file: 'manifest-integration.yml'
+
+variables:
+  GITLAB_CI_REVISION: 943eac764805a486e3ca2538a263ab531fd4c45b

.gitmodules

+[submodule ".gitlab-ci"]
+	path = .gitlab-ci
+	url = ../../../infrastructure/gitlab-ci.git