Test improvements

[rkm]

Possible avenues of investigation:

• Separate unit tests from integration/system
• Remove redundant tests against external dependencies and mock when needed
  • E.g., We don't need to test that every service can publish to RabbitMQ, only a single implementation needs to check this
• Switch to RDMP yaml repo for testing, removing the need for SQL server
• Switch from MySQL to Postgres to match the live environment
• Refactor to allow running all tests in parallel
  • Probably low value initially, as one test suite (DicomRelationalMapper) takes significantly longer to execute than the rest
• Misc
  • Remove all references to Oracle DB (DatabaseType.Oracle / OracleImplementation) - we never intend to enable these