Fix build

[Matesanz]

Problems solved by this PR

This PR fixes two mayor problems I encountered while building this artifact:

• Maven 3.8^ blocks custom repos by default not allowing confluent dependencies to be downloaded.
• Bintray repos (where some dependencies were stored) are no longer active, so original links to dependencies don't work anymore.

How are those problems solved

• Only by modifying pom.xml file.
• Adding Confluent repo to trusted to repositories.
• Migrating from bintray to maven central repository by pinning plugins and dependencies from bintray to their relatives in central maven repository.

Related issues

• Fixes Error when building. #4
• Fixes issue in original jonahharris repo How to build this plugin? jonahharris/kafka-connect-rabbitmq#13
• It also allows this artifact to be built from inside a fresh docker image (not settings.xml needed)