Implement -D flag for ODBC DSN (Data Source Name) support

Summary

The ODBC sqlcmd supports a -D flag that allows connecting using an ODBC Data Source Name (DSN) instead of specifying connection parameters directly.

Current State

• The -D flag is not implemented in go-sqlcmd
• Linux ODBC sqlcmd supports this for using pre-configured DSNs

Requested Behavior

When -D is specified, the -S parameter should be interpreted as a DSN name rather than a server name. The DSN would be looked up from the system's ODBC configuration (e.g., /etc/odbc.ini\ on Linux or ODBC Data Source Administrator on Windows).

Considerations

• go-sqlcmd uses go-mssqldb directly, not ODBC, so implementing DSN support would require:
  • Parsing ODBC ini files to extract connection parameters
  • Or, using CGO to call ODBC APIs (which would add complexity)
• This may require a design discussion to determine the best approach

References

• ODBC sqlcmd usage: -S <DSN_name> -D\ indicates that -S\ refers to a DSN

Start by reviewing the command-line handling for -D and -S and how go-sqlcmd passes connection parameters to go-mssqldb. Compare parsing ODBC ini files with calling ODBC APIs through CGO, then clarify the design choice. Done means -D makes -S resolve a configured DSN on supported systems, with the connection behavior and platform scope defined.