Connector offsets API implementation [DBZ-9083]

Migrated from [DBZ-9083](https://issues.redhat.com/browse/DBZ-9083)

h1. Feature request or enhancement
h2. Which use case/requirement will be addressed by the proposed feature?

This enhancement addresses the need for {*}first-class support for offset management in Kafka Connect{*}, outlined in [KIP-875|https://cwiki.apache.org/confluence/display/KAFKA/KIP-875%3A+First-class+offsets+support+in+Kafka+Connect]. This would allow for:
* Validation of user-provided offsets
* Easier management of offsets from external systems, including:
** Resetting offsets, particularly in staging/development environments that may rapidly change-saves having to create new connectors over and over
** Skipping invalid records not addressed by current error-handling

* Avoiding direct manipulation of Kafka Connect internals i.e. offsets topic in distributed Kafka Connect architecture