message: add changelog about zig 0.9 upgrade
diff: * Add auto-batching to Producer ([#2000](https://github.com/infinyon/fluvio/issues/2000))
  * Add support for 3rd party connectors ([#2027](https://github.com/infinyon/fluvio/pull/2027))
  * Introduce channels into CLI ([#2021](https://github.com/infinyon/fluvio/issues/2021))
  +* Upgrade to Zig 0.9 and LLVM 13 ([#2046](https://github.com/infinyon/fluvio/pull/2046))
  ## Platform Version 0.9.15 - 2021-12-10
  * Migrate Rust crates to edition 2021 ([#1798](https://github.com/infinyon/fluvio/issues/1798))
  