Dell: Throw NoSuchNamespaceException when updating missing namespace

[thswlsqls]

Closes #17270

Summary

• EcsCatalog.setProperties() and removeProperties() leaked the vendor exception com.emc.object.s3.S3Exception (404 NoSuchKey) for a missing namespace.
• Both delegate to updateProperties(), which called loadProperties() with no existence check; loadProperties() does not translate 404, unlike objectMetadata().
• Every sibling catalog supporting namespace properties checks first — InMemoryCatalog, JdbcCatalog, GlueCatalog — as does loadNamespaceMetadata() here. EcsCatalog was the only leak.
• Both signatures already declare throws NoSuchNamespaceException. SupportsNamespaces marks that @throws (optional), which permits not throwing — not leaking a vendor exception.
• Namespace.empty() (root) has no properties object, so it now raises NoSuchNamespaceException rather than S3Exception; only the exception type changes.

The check follows the dominant idiom in this class (listNamespaces(), dropNamespace()):

if (!namespaceExists(namespace)) {
  throw new NoSuchNamespaceException("Namespace %s does not exist", namespace);
}

Testing done

• Added TestEcsCatalog#namespacePropertiesOfMissingNamespace covering both methods; it fails on main with S3Exception.
• ./gradlew :iceberg-dell:check — 26 tests passed.
• dell/ is outside the published REVAPI modules, so no revapi run.