[C++][CI][Packaging][FlightPRC] ODBC macOS DMG installer signing

### Describe the enhancement requested

The Apache Arrow Flight SQL ODBC macOS DMG installer needs to be signed in order for macOS Gatekeeper to allow install.


Acceptance Criteria:
Manual script to sign the macOS DMG installer

Reference comment: https://github.com/apache/arrow/issues/47876#issuecomment-3974162168

### Component(s)

C++, Packaging, FlightRPC