feat(stovepipe): add validate controller forwarding commits to batch

[mnoah1]

Set up empty validate controller. This consumes events from the existing start controller, than forwards them to batch if valid. Here, we can implement additional validation logic on a given commit before passing it forward to a batch.

Also wires this into the existing controller

Why?

Building out overall workflow outlined in https://github.com/uber/submitqueue/blob/main/doc/rfc/stovepipe/workflow.md

What?

Validate step in the outline above

Test Plan

• make local-stovepipe-start
• Insert a message and confirm flow through the steps:

rchestrator-service-1  | 2026-06-16T22:15:23.665Z	DEBUG	consumer/consumer.go:351	processing delivery	{"controller": "start", "topic_key": "start", "message_id": "manual-1781648123538", "partition_key": "github.com/uber/cadence", "attempt": 1}
orchestrator-service-1  | 2026-06-16T22:15:23.665Z	INFO	start_controller	start/start.go:91	received change event	{"uri": "git://github.com/uber/cadence/refs/heads/main/abc123def456", "attempt": 1, "partition_key": "github.com/uber/cadence"}
orchestrator-service-1  | 2026-06-16T22:15:23.665Z	DEBUG	queue_mysql.message_store	mysql/message_store.go:72	inserting messages	{"topic": "validate", "count": 1, "visible_after": 0}
orchestrator-service-1  | 2026-06-16T22:15:23.669Z	DEBUG	queue_mysql.message_store	mysql/message_store.go:125	inserted messages	{"topic": "validate", "count": 1}
orchestrator-service-1  | 2026-06-16T22:15:23.669Z	DEBUG	queue_mysql.publisher	mysql/publisher.go:65	published message	{"topic": "validate", "message_id": "git://github.com/uber/cadence/refs/heads/main/abc123def456"}
orchestrator-service-1  | 2026-06-16T22:15:23.669Z	INFO	start_controller	start/start.go:106	published commit to validate	{"uri": "git://github.com/uber/cadence/refs/heads/main/abc123def456", "topic_key": "validate"}
orchestrator-service-1  | 2026-06-16T22:15:23.674Z	DEBUG	consumer/consumer.go:479	message processed successfully	{"controller": "start", "topic_key": "start", "message_id": "manual-1781648123538", "partition_key": "github.com/uber/cadence", "attempt": 1, "elapsed_ms": 4}
orchestrator-service-1  | 2026-06-16T22:15:23.757Z	DEBUG	queue_mysql.message_store	mysql/message_store.go:217	fetched messages	{"topic": "start", "partition_key": "github.com/uber/cadence", "count": 1}
orchestrator-service-1  | 2026-06-16T22:15:23.767Z	DEBUG	consumer/consumer.go:351	processing delivery	{"controller": "validate", "topic_key": "validate", "message_id": "git://github.com/uber/cadence/refs/heads/main/abc123def456", "partition_key": "github.com/uber/cadence", "attempt": 1}
orchestrator-service-1  | 2026-06-16T22:15:23.767Z	INFO	validate_controller	validate/validate.go:89	received change event	{"uri": "git://github.com/uber/cadence/refs/heads/main/abc123def456", "attempt": 1, "partition_key": "github.com/uber/cadence"}
orchestrator-service-1  | 2026-06-16T22:15:23.767Z	DEBUG	queue_mysql.message_store	mysql/message_store.go:72	inserting messages	{"topic": "batch", "count": 1, "visible_after": 0}
orchestrator-service-1  | 2026-06-16T22:15:23.770Z	DEBUG	queue_mysql.message_store	mysql/message_store.go:125	inserted messages	{"topic": "batch", "count": 1}
orchestrator-service-1  | 2026-06-16T22:15:23.770Z	DEBUG	queue_mysql.publisher	mysql/publisher.go:65	published message	{"topic": "batch", "message_id": "git://github.com/uber/cadence/refs/heads/main/abc123def456"}
orchestrator-service-1  | 2026-06-16T22:15:23.770Z	INFO	validate_controller	validate/validate.go:104	published commit to batch	{"uri": "git://github.com/uber/cadence/refs/heads/main/abc123def456", "topic_key": "batch"}
orchestrator-service-1  | 2026-06-16T22:15:23.774Z	DEBUG	consumer/consumer.go:479	message processed successfully	{"controller": "validate", "topic_key": "validate", "message_id": "git://github.com/uber/cadence/refs/heads/main/abc123def456", "partition_key": "github.com/uber/cadence", "attempt": 1, "elapsed_ms": 3}

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