refactor: consume the config-file writer from stackable-operator

Replace the vendored java-properties/Hadoop-XML writer
(rust/operator-binary/src/config/writer.rs) with
stackable_operator::v2::config_file_writer, which hosts this exact file
(moved there verbatim via operator-rs #1217 on the smooth-operator branch;
hdfs's copy was the canonical source). Drop the now-unused java-properties
and xml dependencies.

No behaviour change; rendered output is byte-identical by construction
(same code, new home).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: adwk67