[FEATURE] Opt-in auto-create relational entity store schema on startup

### Describe the feature

When Gravitino uses an external relational database backend (e.g., MySQL/PostgreSQL) for the relational entity store, allow the server to automatically initialize the required schema/tables on startup (opt-in).

### Motivation

Today, operators must manually run schema/upgrade SQL scripts. In dev/test environments it is easy to hit missing-table errors after upgrading or starting the server against a fresh database (schema not initialized). Auto-creating the schema (opt-in) can significantly improve the developer/test experience and reduce manual setup steps.

### Describe the solution

Introduce a new configuration property:

- `gravitino.entity.store.relational.autoCreateSchema` (default: `false`)

When enabled, and the JDBC backend is **non-embedded**, the server checks whether the schema exists; if not, it executes the current schema initialization script under:

- `${GRAVITINO_HOME}/scripts/{mysql,postgresql}/schema-${CURRENT_SCRIPT_VERSION}-*.sql`

Safety / constraints:

- Embedded H2 behavior remains unchanged.
- Unsupported JDBC types should be skipped with a warning.
- If the schema script is missing, skip with a warning (no startup failure).

### Additional context

- Related PR (implementation): https://github.com/apache/gravitino/pull/10819
- Suggested test:
- `./gradlew :core:test`
- Start server with relational store backed by MySQL/PostgreSQL and `gravitino.entity.store.relational.autoCreateSchema=true`, ensure tables are created and server starts without missing-table errors.

Review related PR #10819 and the relational entity store startup path. Run ./gradlew :core:test, then test with MySQL or PostgreSQL and gravitino.entity.store.relational.autoCreateSchema=true. Done means the required tables are created for supported non-embedded backends without missing-table startup errors, while unsupported types and missing scripts only warn.

Written by the indexing model from the issue text.