Add support for service load plugin discovery

[yeikel]

Hi team,

I am trying to leverage KIP-898: Modernize Connect plugin discovery but both the source and the Sink connectors are missing the mandatory setup:

Sample error

org.apache.kafka.connect.errors.ConnectException: One or more plugins are missing ServiceLoader manifests may not be usable with plugin.discovery=service_load: [
file:/usr/share/confluent-hub-components/confluentinc-kafka-connect-elasticsearch/ io.confluent.connect.elasticsearch.ElasticsearchSinkConnector sink 14.1.1
file:/usr/share/java/acl/ io.confluent.connect.json.JsonSchemaConverter converter undefined