docs(jdbc): add "JAVA SQL Interface.png" diagram for JDBC API hierarchy

What
- Added visual diagram file **JAVA SQL Interface.png**.
- Shows the interface and class hierarchy in the `java.sql` package.
- Highlights key JDBC interfaces like:
  - `Driver`, `Connection`, `Statement`, `PreparedStatement`, `CallableStatement`
  - `ResultSet`, `ResultSetMetaData`
  - `DatabaseMetaData`
- Illustrates how concrete driver implementations (e.g., SQLite, MySQL) extend these interfaces.

Why
- Provides a quick reference to the layered JDBC architecture.
- Helps developers understand the relationship between core interfaces.
- Bridges theoretical learning with practical API usage in JDBC examples.
- Aids in debugging by clarifying which object type to use for different tasks.

How
- Created diagram capturing `java.sql` contract interfaces.
- Mapped out dependencies:
  - `Connection` obtained from `DriverManager`.
  - `Statement`/`PreparedStatement` created via `Connection`.
  - `ResultSet` returned from executing queries.
- Ensured clear labeling of interfaces vs. implementing classes.

Key Notes
- JDBC heavily relies on interface-driven design for driver independence.
- Different database vendors (Oracle, SQLite, MySQL) provide their own implementations.
- Developers only interact with standard interfaces → ensures portability.
- `PreparedStatement` and `CallableStatement` extend `Statement`.

Real-life Applications
- Onboarding new team members: speeds up understanding of JDBC APIs.
- Training material: improves clarity during workshops.
- Quick lookup during database module implementation.
- Serves as documentation alongside code demos (`Database`, `Statements`, `Call`, etc.).

Future Improvements
- Add color-coded grouping (Connections, Statements, Metadata).
- Extend diagram with JDBC 4.0+ enhancements (like `RowSet`).
- Include typical usage flow arrows for better context.

Signed-off-by: https://github.com/Someshdiwan <[email protected]>

Author: Someshdiwan