[elixir] Extended configuration options

[fresh-borzoni]

Search before asking

• I searched in the issues and found nothing similar.

Description

depends on #452

Add writer tuning (acks, retries, idempotence, buffer size, inflight limit), scanner tuning (prefetch, concurrency, poll records, fetch bytes), security/SASL config, connect timeout.

Willingness to contribute

• I'm willing to submit a PR!