Docs: JDBC driver should go to Oracle connector dir

Currently, we describe in the upstream docs for the DBZ Oracle connector, that the driver JAR (and Xstream JAR) should go to kafka/libs. Let's rather say that they should go into the plugin directory for the connector (i.e. next to debezium-connector-oracle-x.y.z.jar). Also the order in the "obtaining the driver section" isn't ideal, because it suggests to do a restart and only then obtain the JDBC driver.

I suggest to fold that section into the previous procedure:

1. Download the Debezium Oracle connector plug-in archive.
2. Extract the files into your Kafka Connect environment.
3. Download the Oracle JDBC driver from Maven Central and extract it into the directory with the connector JAR files
4. Add the directory with the JAR files to Kafka Connect’s plugin.path.
5. Restart your Kafka Connect process to pick up the new JAR files.

Note the step "Configure the connector and add the configuration to your Kafka Connect cluster." should not be part of this procedure, which only is about installing/deploying the connector.

Also note the version for the JDBC driver should be sourced from an (Antora) variable and it should reflect what is used by Debezium for testing (in particular, it's independent of the DB server version).