Gzip compression and upload size limits

DecisionLogPlugin.DecisionLogs.sendToService POSTs the entire batch as uncompressed JSON regardless of size. OPA Go gzip-compresses decision-log batches and honors reporting.upload_size_limit_bytes, splitting batches that exceed it. The Java SDK should match both behaviors to keep operator expectations consistent and reduce bandwidth.

• Gzip the request body before sending; set Content-Encoding: gzip.
• Honor reporting.upload_size_limit_bytes — chunk the batch into multiple POSTs when it exceeds the cap (size is measured after compression to match OPA Go).
• If a single event exceeds the cap, log a warning and either send it on its own (with a flag) or drop it per a configurable policy.
• Tests covering: small batch single POST, large batch chunked into multiple POSTs, oversized single event handled.

Start at DecisionLogPlugin.DecisionLogs.sendToService and trace how batches are serialized, posted, and configured. Check how reporting.upload_size_limit_bytes is exposed, then add coverage for a compressed small batch, compressed size-based chunking, and an oversized single event. Done means requests use gzip, respect the cap, and apply a defined policy for oversized events.