ci: add yamllint (#6682)

adds yaml linting to CI and applies rules to existing yaml files.

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-6682-ci-add-yamllint-2aa6d73d365081b4b67ae9d9cc86760f)
by [Unito](https://www.unito.io)

.github/workflows/ci-yaml-validation.yaml

@@ -0,0 +1,33 @@
+name: "CI: YAML Validation"
+description: "Validates YAML syntax and style using yamllint with relaxed rules"
+
+on:
+  push:
+    branches:
+      - main
+    paths:
+      - '**/*.yml'
+      - '**/*.yaml'
+  pull_request:
+    paths:
+      - '**/*.yml'
+      - '**/*.yaml'
+
+jobs:
+  yaml-lint:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v5
+
+      - name: Set up Python
+        uses: actions/setup-python@v5
+        with:
+          python-version: '3.x'
+
+      - name: Install yamllint
+        run: |
+          python -m pip install --upgrade pip
+          python -m pip install yamllint
+
+      - name: Validate YAML syntax and style
+        run: ./scripts/cicd/check-yaml.sh