Task: Setup a GitHub Actions CI pipeline for PR validation

[lhotari]

After #3 is completed, it would be useful to setup a GitHub Actions CI pipeline for PR validation.
The main flow could follow Pulsar CI with all unnecessary steps removed.

1. Copy https://github.com/apache/pulsar/blob/master/.github/workflows/pulsar-ci.yaml as .github/workflows/pulsar-sql-ci.yaml and remove all unnecessary parts. It's sufficient to build and test with Java 21. No need for Java 17 & Java 21 co-existence as there is in Pulsar Ci.
2. Copy https://github.com/apache/pulsar/blob/master/.github/changes-filter.yaml and adapt it
3. Copy https://github.com/apache/pulsar/tree/master/build scripts and adapt.