Kafka connector fallback hosts need to be explicitly added to the connector properties

[mclark-ably]

When using the Kafka connector fallback hosts aren't tried and the batch publish fails and goes to dlq (if configured) if the request times out

connector          | io.ably.lib.types.AblyException$HostFailedException: java.lang.Exception: connect timed out
connector          |    at io.ably.lib.types.AblyException.fromErrorInfo(AblyException.java:32)
connector          |    at io.ably.lib.types.AblyException.fromErrorInfo(AblyException.java:25)
connector          |    at io.ably.lib.http.Http$Request.sync(Http.java:45)
connector          |    at io.ably.lib.http.HttpPaginatedQuery.exec(HttpPaginatedQuery.java:56)
connector          |    at io.ably.lib.http.HttpPaginatedQuery.exec(HttpPaginatedQuery.java:40)
connector          |    at io.ably.lib.rest.AblyBase.request(AblyBase.java:288)
connector          |    at com.ably.kafka.connect.client.DefaultAblyBatchClient.sendBatches(DefaultAblyBatchClient.java:188)
connector          |    at com.ably.kafka.connect.client.DefaultAblyBatchClient.publishBatch(DefaultAblyBatchClient.java:90)
connector          |    at com.ably.kafka.connect.batch.BatchProcessingThread.run(BatchProcessingThread.java:36)
connector          |    at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
connector          |    at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
connector          |    at java.base/java.lang.Thread.run(Thread.java:834)
connector          | Caused by: java.lang.Exception: connect timed out
connector          |    ... 11 more```

it appears in the connector config that the list of fallbacks is an empty list 
`connector          |    client.fallback.hosts = []`

The fallback host client option is set to this which overwrites the default fallback hosts which would be set on a Java SDK client if the fallback host option was not set

https://github.com/ably/kafka-connect-ably/blob/4d782f2e21a35521776aaee12387329ce4f0ad6c/src/main/java/com/ably/kafka/connect/config/ChannelSinkConnectorConfig.java#L218C9-L218C84

Workaround: Add the fallbacks explicitly to the connector config

┆Issue is synchronized with this [Jira Task](https://ably.atlassian.net/browse/ECO-4853) by [Unito](https://www.unito.io)