Consider using jib plugin instead of docker-maven-plugin

[vkorenev]

Both this project and examples in cloudstateio/kotlin-support use Maven to build and push container images. However, they use different Maven plugins for that.
It might be good to use the same plugin in both places. jib-maven-plugin might be a better choice since it does not require Docker to be installed.
It might be good to unify the Maven build phase for pushing the image as well. The build phase for kotlin-support was changed to deploy by cloudstateio/kotlin-support#18. However, this project builds and pushes the image at the package phase.

[vkorenev]

cloudstate/kotlin-support no longer uses maven build. However, it might be still good to switch to jib plugin in this project.