Refactor Registry Database Integration Strategy

NiFi Registry uses Spring JDBC for simplifying some aspects of relational database integration, which eliminates boilerplate JDBC handling. However, Spring JDBC does not provide a unified approach for handling different database vendors. The current implementation strategy supports several different relational databases, but does not lend itself to others, such as Microsoft SQL Server and Oracle Database.

MyBatis is one potential solution that is licensed under ASLv2 and provides an ORM layer with optional vendor-specific overrides where needed. MyBatis also supports using direct SQL as opposed to some other intermediate translation layer.

Other potential solutions exist that could be evaluated, but some solution is necessary before support for additional database types can be implemented.