[MINOR-UPDATE]: Drop conjars repo and revert ci.yml runner image to ubuntu-latest (#2782)
* Add RPC and HTTP bind address lines to drill-override-example.conf.
* Revert ci.yml to ubuntu-latest.
* Move Splunk Maven repository declaration to contrib/storage-splunk/pom.xml.
* Upgrade parquet to 1.12.3 and parquet-format to 2.9.0.
* Drop conjars repository.
* Set drill.version in drill-udf/pom.xml to 1.21.0.
