Automate license headers validation

**Background**

Every new source file in the cloud pipeline repository should contain a license header. As long as it can be easily forgotten to be added it can be helpful to automate license headers validation or even license header fixing.

**Approach**

There is a neat [license-gradle-plugin](https://github.com/hierynomus/license-gradle-plugin) which can be used in our CI process to fail the build if some of the license headers are missing or even add/update them automatically right in the pull request.

Start by reviewing the repository's CI and build configuration, then read the linked license-gradle-plugin documentation to understand validation and automatic header updates. Define whether the workflow should only fail on missing headers or also update pull requests; done means new source files are checked consistently in CI.

Written by the indexing model from the issue text.