KIP-738 — Removal of Connect's internal converter properties

Accepted Kafka 3.0 Connect

Makes the deprecated `internal.key.converter` and `internal.value.converter` Connect worker properties fatal on startup so workers immediately fail rather than silently producing corrupted internal topic data. Workers configured with a non-default internal converter cannot read internal topic data written by workers with a different converter, leading to hard-to-diagnose data corruption.

Details