Set Replica Identity Decisions Endpoint

Record the customer's per-table decisions for ARD-999 preflight.

Every entry in request_body.decisions must:

• have a key that matches a discovered no-replication-identity table for this connector ("<database>.<schema>.<table>" FQN), and
• have a value of "exclude", "add_pk", or "replica_identity_full".

Validation fails loud (400) on any mismatch — silent acceptance of keys that don't match would let a typo persist as a dead entry that looks correct in the connector record but has no effect at engine setup time. Tables that exist in the discovered no-replication- identity list but are absent from decisions revert to the default "exclude" (the pre-ARD-999 behavior). This endpoint is a full replace: submit the complete decision set for every table that should keep a non-default decision, because omitted FQNs revert to "exclude" even if a prior PUT recorded a different decision.

Response carries the updated connector with the refreshed replica_identity_preflight block (same shape as GET) so the CLI and the web wizard can render the post-write state without a follow- up round-trip.