feat(server): add PostgreSQL persistence profile

[Aias00]

Summary

Adds PostgreSQL 16+ support for the existing Studio MyBatis-Plus persistence layer.

• adds the PostgreSQL JDBC runtime driver and Testcontainers test dependencies
• adds a postgres Spring profile that initializes the PostgreSQL schema
• adds a PostgreSQL DDL equivalent for all current Studio persistence entities
• adds a PostgreSQL integration test for general settings and data-source CRUD
• documents external PostgreSQL deployment configuration

Validation

• mvn -Dtest=PostgreSqlSettingsRepositoryIntegrationTest test
  • compiles successfully; the Testcontainers test is skipped locally because this machine's Docker Java client reports API 1.32 while the Docker daemon requires 1.40
• manual PostgreSQL 16 validation through Docker CLI:
  • started Studio with the postgres profile
  • created a data source through the settings API
  • restarted Studio and confirmed the data source was still returned
  • confirmed one persisted rmq_data_source row in PostgreSQL

Closes #956

[Copilot]

Copilot was unable to review this pull request because the user who requested the review has reached their quota limit.

[Aias00]

Superseded by #980, which now contains this change.