Postgres support

• Build pytest fixture to test with sqlite and pg
  • tempdir fixture with and without sqlite files
  • .autosubmitrc builder fixture
  • fixture to copy SQLite db files content to a Postgres instance
  • mock session
• Centralize all SQL operations in one module with "repositories" (interfaces following DDD principles)
  • autosubmit.db
  • as_times.db
  • structures_xxxx.db (skipping it for now, using autosubmit.database.db_structure instead)
  • job_data_xxxx.db
  • job_packages.db
  • graph_xxxx.db
• Refactor classes that directly call sqlite3 or sqlalchemy
• Support changes on autosubmit!426
  • Support autosubmit.database.tables module
  • Refactor session to handle pooling in multithreading workers of Gunicorn