feat(sink): add Redis Streams sink

[psteinroe]

Summary

• Add RedisStreamsSink that publishes events to Redis Streams using XADD
• Sends event.payload as JSON in a single "payload" field
• Supports dynamic stream routing via event metadata
• Supports optional max_len for approximate stream trimming (MAXLEN ~)

Configuration

sink:
  type: redis-streams
  url: redis://localhost:6379
  stream_name: events  # optional default stream
  max_len: 10000       # optional trimming

Routing

The target stream is resolved from:

1. stream field in event metadata (from subscription's metadata or metadata_extensions)
2. Fallback to stream_name in config

-- Dynamic stream from table name
metadata_extensions = '[{"json_path": "stream", "expression": "''events:'' || tg_table_name"}]'