Deprecate and remove Connect's redundant task configurations retrieval endpoint

A new endpoint (GET /connectors/{connector}/tasks-config) was added to Kafka Connect's REST API to expose task configurations in KIP-661. However, the original patch for Kafka Connect's REST API had already added an endpoint (GET /connectors/{connector}/tasks) to retrieve the list of a connector's tasks and their configurations (ref - https://github.com/apache/kafka/pull/378 , https://issues.apache.org/jira/browse/KAFKA-2369) and this was missed in KIP-661. We can deprecate the endpoint added by KIP-661 in 3.7 (the next minor AK release) and remove it in 4.0 (the next major AK release) since it's redundant to have two separate endpoints to expose task configurations. Related discussions in https://github.com/apache/kafka/pull/13424#discussion_r1144727886 and https://issues.apache.org/jira/browse/KAFKA-15377