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)

scripts/cicd/check-yaml.sh

@@ -0,0 +1,14 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+ROOT_DIR="$(git rev-parse --show-toplevel)"
+cd "$ROOT_DIR"
+
+mapfile -t yaml_files < <(git ls-files '*.yml' '*.yaml')
+
+if [[ ${#yaml_files[@]} -eq 0 ]]; then
+  echo "No YAML files found to lint"
+  exit 0
+fi
+
+yamllint --config-file .yamllint "${yaml_files[@]}"