[C++] [FlightSQL][ODBC]: Replace `ODBC` namespace with `namespace arrow::flight::sql::odbc`

### Describe the enhancement requested

- Replace `ODBC` namespace with `namespace arrow::flight::sql::odbc` in `odbc_impl`

Parent issue: https://github.com/apache/arrow/issues/30622

### Component(s)

C++, FlightRPC