make kafka topic creation and partition config configurable via env vars

[VINODvoid]

Description

Addresses two open review comments on #220.

KafkaOutputSink had hardcoded num_partitions=3 and replication_factor=3 in ensure_topic(), and topic auto-creation always ran unconditionally on startup. This makes both
configurable via environment variables.

OSPREY_KAFKA_AUTO_CREATE_TOPIC (default: true) — set to false for deployments that manage Kafka topics via Terraform or other IaC tooling.

OSPREY_KAFKA_NUM_PARTITIONS (default: 1) and OSPREY_KAFKA_REPLICATION_FACTOR (default: 1) — replaces the hardcoded 3 values. Defaults to 1 so single-broker local
setups (docker-compose) don't fail silently on topic creation. Production deployments can override via env.

Both are read in sink_register.py and passed into KafkaOutputSink.__init__, following the same pattern as all other Kafka config in this codebase.

Branch based on hailey/confluent-kafka.

Checklist

• Tests pass locally
• uv run ruff check . passes (no unused imports or other lint errors)
• uv tool run fawltydeps --check-unused --pyenv .venv passes (no unused dependencies)
• Updated CHANGELOG.md with my changes, if applicable

[VINODvoid]

@haileyok hey, took a stab at addressing the review feedback from @ThisIsMissEm and @chimosky — opened a branch off yours if you want to take a look!

[haileyok]

wow, thank you! I'll take a look at this later today, very much appreciate this!!!