Build, Kafka-Connect: Disable publishing for empty grouping project

[dramaticlly]

Running into publish issue with org.apache.iceberg:iceberg-kafka-connect as I realized there's name collision in top level and nested project. Disabled top level one here to allow a happy publish

• top level: https://github.com/apache/iceberg/blob/main/settings.gradle#L192
• nested: https://github.com/apache/iceberg/blob/main/settings.gradle#L200

CC @bryanck @amogh-jahagirdar @huaxingao

Local test to verify the new behavior

$ ./gradlew :iceberg-kafka-connect:publishToMavenLocal :iceberg-kafka-connect:iceberg-kafka-connect:publishToMavenLocal 2>&1 | grep -E "(publishApache|publishTo|SKIPPED|disabled)" 

> Task :iceberg-kafka-connect:generatePomFileForApachePublication SKIPPED
> Task :iceberg-kafka-connect:generateMetadataFileForApachePublication SKIPPED
> Task :iceberg-kafka-connect:publishApachePublicationToMavenLocal SKIPPED
> Task :iceberg-kafka-connect:publishToMavenLocal SKIPPED
> Task :iceberg-kafka-connect:iceberg-kafka-connect:publishApachePublicationToMavenLocal
> Task :iceberg-kafka-connect:iceberg-kafka-connect:publishToMavenLocal

[dramaticlly]

also I think it will close #14549

[huaxingao]

LGTM

[bryanck]

LGTM, thanks for catching this @dramaticlly . Also, thanks for the review @huaxingao !