feat(yaml_lint): Added job yaml lint for checking yaml files

defaults to checking subfolder/.gitlab-ci.yml.

 Changes to be committed:
	modified:   .gitlab-ci.yml
	new file:   yaml_lint/.gitlab-ci.yml
	new file:   yaml_lint/.yamllint.yaml
	new file:   yaml_lint/README.md
	new file:   yaml_lint/requirements.txt

issue #1

.gitlab-ci.yml

@@ -8,11 +8,20 @@ stages:
     - sync
 
 include:
+  - local: $JOB_ROOT_DIR/yaml_lint/.gitlab-ci.yml
   - local: $JOB_ROOT_DIR/conventional_commits/.gitlab-ci.yml
   - local: $JOB_ROOT_DIR/git_push_mirror/.gitlab-ci.yml
   - local: $JOB_ROOT_DIR/gitlab_release/.gitlab-ci.yml
 
 
+gilab-ci.yml Lint (python 3.6):
+    variables:
+        YAML_LINT_PATH: "/*/.gitlab-ci.yml"
+    extends:
+        - .yaml_lint_defaults
+    image: python:3.6-slim
+
+
 Gitlab Release:
     variables:
         MY_COMMAND: ./sub-folder_changlog.sh
@@ -20,7 +29,6 @@ Gitlab Release:
         - .gitlab_release
 
 
-
 Github (Push --mirror):
     variables:
         GIT_SYNC_URL: "https://$GITHUB_USERNAME_ROBOT:$GITHUB_TOKEN_ROBOT@github.com/NoFussComputing/gitlab-ci.git"