Improve markdownlint coverage (#7075)

Now markdownlint covers ./README.md and md files under ./docs only.
However we have a lot of md files under different directories also.
This enables markdownlint for other md files also.

.gitlab-ci/lint.yml

@@ -64,9 +64,10 @@ markdownlint:
   tags: [light]
   image: node
   before_script:
-    - npm install -g markdownlint-cli
+    - npm install -g markdownlint-cli@0.22.0
   script:
-    - markdownlint README.md docs --ignore docs/_sidebar.md
+    # TODO: Remove "grep -v" part to enable markdownlint for all md files
+    - markdownlint $(find . -name "*.md" | grep -v .github | grep -v roles | grep -v contrib/terraform | grep -v contrib/vault | grep -v contrib/network-storage) --ignore docs/_sidebar.md --ignore contrib/dind/README.md
 
 ci-matrix:
   stage: unit-tests