[Subtask] Add Semantic Model OpenAPI specification in Gravitino

### Describe the subtask

Add the OpenAPI specification for Semantic Model lifecycle REST APIs, including list, create, load, alter, and drop endpoints and their request and response schemas.

Server implementation, clients, and generated SDK changes are out of scope.

### Parent issue

#12209

Locate the repository's existing OpenAPI specifications and read parent issue #12209 for the Semantic Model context. Add specifications for list, create, load, alter, and drop lifecycle endpoints, including request and response schemas; done means the API specification is complete without server, client, or generated SDK changes.

Written by the indexing model from the issue text.