[Subtask] Add Semantic Model create and load REST APIs in Gravitino

### Describe the subtask

Add REST APIs for creating and loading Semantic Models, including endpoint request and response DTOs, conversion, server routing, exception handling, and focused tests.

The APIs use the reusable Semantic Model definition DTOs and Core create/load operations. List, alter, drop, OpenAPI, and clients are out of scope.

### Parent issue

#12209

Start by locating existing server REST endpoints and the reusable Semantic Model definition DTOs, then trace the Core create/load operations. Review the endpoint request and response DTOs, conversion, routing, exception handling, and focused tests. Done means create and load REST APIs work with coverage for the supported responses and errors, while list, alter, drop, OpenAPI, and clients remain out of scope.

Written by the indexing model from the issue text.