[Improvement] 1.3.1 release notes must call out the connector behavior changes

### What would you like to be improved?

### Why

Three changes going into 1.3.1 alter behavior for deployments already
running 1.3.0. Each of them looks like a healthy cluster after the
upgrade and fails later, which is the worst shape for an operator to
debug. They need to be stated in the release notes rather than
discovered.

### What needs to be in the notes

- [ ] **The OAuth credential is no longer written into the generated
CREATE CATALOG.** Multi-node deployments using oauth2 must configure
the environment-variable mapping on the coordinator and every worker
before upgrading. Without it, catalogs still register and metadata
still lists, so the cluster appears fine, and every query that
reaches a worker fails.

- [ ] **Iceberg REST routing is enabled by default in the Trino
connector.** A deployment on a released 1.3 server sees Iceberg
catalogs change behavior. The escape hatch is
`gravitino.iceberg.rest-routing-enabled`.

- [ ] **The Spark connector loses its silent fallback to hive/jdbc
translation** when no Iceberg REST endpoint is discovered, matching
the Trino behavior. Spark needs the same escape hatch, and both
belong in the notes as behavior changes.

### Related

- Spark connector items: #12687

### How should we improve?

_No response_