[Subtask] Add Semantic Model create and load persistence in Gravitino

### Describe the subtask

Add relational persistence for creating and loading Semantic Models. This includes persistent objects and serialization, the required mappers and SQL providers, metadata service insert/get operations, JDBC backend routing, and H2/MySQL/PostgreSQL tests.

Create must persist the identity and initial version atomically, and load must preserve the complete Semantic Model definition.

List, alter, drop, cascade deletion, garbage collection, version retention, REST APIs, and clients are out of scope.

### Parent issue

#12209

Start with the metadata service create/get operations, relational persistence and serialization requirements, then trace JDBC backend routing. Done means create atomically persists the Semantic Model identity and initial version, load preserves the complete definition, and H2/MySQL/PostgreSQL tests cover both operations.

Written by the indexing model from the issue text.