Atomically upserts up to 500 signal-to-metrics configurations at once. If any item
fails validation or cannot be written, the entire batch is rejected and no
configurations are changed.

This endpoint is designed for Infrastructure-as-Code (IaC) workflows (Terraform,
the operator, CLI scripts). Rules are matched by their origin values across
repeated invocations, making the operation idempotent.

This endpoint accepts request bodies up to 2 MB (vs. the 256 KB default for other
endpoints) to accommodate batched payloads of up to 500 rules per request.