Add datree-validation.yml

[datreeio]

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[what-the-diff]

PR Summary

• Trigger workflow on pull_request events
  The workflow initiates when a pull request is made.
• Check and identify changed YAML files
  The repository is checked for any changes in YAML files.
• Install Datree CLI tool
  If any changes are detected, the Datree CLI tool is installed. It helps assess and validate Kubernetes configuration files according to the organization's policies.
• Validate Kubernetes config files
  With the --only-k8s flag, the changed files are validated to ensure they adhere to the set policies.