[CICD] Add Clea OS gitlab-ci and 'layers-integration' steps

* This is necessary to perform automatic commit SHAs integration in
 'meta-seco-clea-os' SRCREV.conf file.

.gitlab-ci @ 1f35d1d7

+Subproject commit 1f35d1d7f69f00d10e215daf07ef880dd8f7b04c

.gitlab-ci.yml

+---
+# ---------------------------------------------------------------------------------------
+# Include the default CI steps from the gitlab-ci repo
+# ---------------------------------------------------------------------------------------
+include:
+  - project: '${CI_PROJECT_ROOT_NAMESPACE}/infrastructure/gitlab-ci'
+    ref: 1f35d1d7f69f00d10e215daf07ef880dd8f7b04c
+    file: 'layers-integration.yml'
+
+variables:
+  GITLAB_CI_REVISION: 1f35d1d7f69f00d10e215daf07ef880dd8f7b04c
+  # FIXME: This is only necessary due to the following GitLab limitation:
+  # https://gitlab.com/gitlab-org/gitlab/-/issues/209904
+  # As soon as this gets fixed upstream, the hard-coded branch name should be removed.
+  BB_RECIPE_NAME: seco-touchcal-conv

.gitmodules

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